The revelation came as leading congressional Democrats demanded that the administration turn over documentation about the matter and calls for impeachment grew.
President Trump personally ordered his staff to freeze more than $391 million in aid to Ukraine in the days before he pressed the new Ukrainian president to investigate the Democrats’ leading presidential candidate, two senior administration officials said Monday.
Mr. Trump issued his directive to Mick Mulvaney, the acting White House chief of staff, who conveyed it through the budget office to the Pentagon and the State Department, which were told only that the administration was looking at whether the spending was necessary, the officials said.
The timing of the decision to block the aid and Mr. Trump’s personal involvement, which were first reported by The Washington Post, add vital new elements to the raging debate over the president’s effort to persuade Ukraine to examine unsubstantiated corruption allegations involving former Vice President Joseph R. Biden Jr. and his son Hunter Biden.
The revelation came as leading congressional Democrats demanded that the administration turn over documentation about the matter. Even before news of Mr. Trump’s involvement in freezing the aid, a flood of Democrats had said that the president’s actions could warrant impeachment.
Full List: Who Supports an Impeachment Inquiry Against Trump?
More than 140 House Democrats and one Independent have said they now support impeachment proceedings.
Several House Democrats from more moderate districts who had long resisted such a move added their voices on Monday to calls for an inquiry that could lead to charges of high crimes and misdemeanors against the president.
Mr. Trump, buffeted by questions earlier in the day at the United Nations about his conduct, denied that he withheld the aid from Ukraine in an attempt to press President Volodymyr Zelensky of Ukraine to dig up dirt on the former vice president.
“No, I didn’t — I didn’t do it,” Mr. Trump told reporters. But just moments before, he suggested that there would be nothing wrong with linking American funding for Ukraine, a former Soviet republic that is fighting Russian-backed separatists, to a corruption inquiry about Mr. Biden and his family.
“Why would you give money to a country that you think is corrupt?” Mr. Trump said.
It was one of a series of whipsawing declarations Mr. Trump made throughout the day on Monday as he defended himself, vilified the Bidens and appeared by turns eager and reluctant to reveal the facts at the root of the allegations. Mr. Trump first said he hoped that the transcript of a July 25 phone call he had with Mr. Zelensky would be released, claiming that it would exonerate him, only to angrily deny moments later that he had committed to doing so.
“I hope you get to see it soon,” Mr. Trump said, before arguing that making the transcript public would set a bad precedent — a position that one person familiar with White House deliberations said was being advanced by Secretary of State Mike Pompeo.
Mr. Biden chimed in via the president’s favorite social media platform, Twitter, responding to Mr. Trump’s dismissal of charges of misconduct by writing, “So release the transcript of the call then.”
Mr. Trump has acknowledged raising Mr. Biden and the corruption questions with Mr. Zelensky in the July 25 telephone call. People familiar with the conversation said Mr. Trump repeatedly urged his counterpart to speak with Rudolph W. Giuliani, the president’s personal lawyer, who has been pushing Ukraine aggressively to look into the Bidens and any contacts that the previous government in Kiev had with Democrats during the 2016 campaign.
Mr. Trump did not discuss the delay in the military assistance on the July 25 call with Mr. Zelensky, according to people familiar with the conversation. A Ukrainian official said Mr. Zelensky’s government did not learn of the delay until about one month after the call.
Congressional Democrats have said that if the president really pressured Ukraine for dirt on a domestic political rival, it could be an impeachable offense whether or not he tied the demand to American aid. But if evidence emerges that the president linked the two, it would most likely bolster the case of critics who call that an abuse of power.
The decision to hold back the aid, which had been approved by Congress, came at a time when the president was looking for ways to curb a variety of foreign assistance programs, and some aides at least initially saw it in that broader context. But Mr. Trump singled out Ukraine as a place he considered corrupt and railed about wasting money there, according to people who heard him discuss the matter, and he questioned the aid package for weeks.
The president asked advisers how to think about Mr. Zelensky, a former comedian outside the Ukrainian establishment who was largely unknown to American policymakers and had shown little interest in Mr. Giuliani’s calls for investigations related to American politics.
It soon became clear that the Ukraine aid freeze was different from the hold placed on other programs. Even after other foreign aid was restored, the money for Ukraine remained blocked.
The suspension of the aid caused confusion and frustration in both Washington and Kiev for months. Mr. Zelensky and other Ukrainian officials were mystified and complained to visiting American lawmakers. For five years, Russia has sponsored separatists in eastern Ukraine, and the government in Kiev had relied on American and European security aid.
American government officials were left in the dark, as well. When staff members at the State and Defense Departments who work on issues related to Ukraine learned of the holds in July, they were puzzled and alarmed, according to current and former government officials familiar with the situation.
Pentagon officials tried to make a case to the White House that the Ukraine aid was effective and should not be looked at in the same manner as other aid. But when those arguments were ignored, and when the other aid was allowed to move forward, the Pentagon officials began to wonder about the White House’s skepticism, a former official said.
The assistance came in two pots overseen by different agencies — $250 million from the Defense Department’s Ukraine Security Assistance Initiative and $141 from the State Department’s foreign military financing program. The funds were intended to help train and equip Ukrainian forces in their fight to stave off Russian incursion.
Congressional committees had approved the defense assistance to the Ukrainian military in two tranches — the first in early April and the second in early June, shortly after the Pentagon submitted the spending for approval, according to the officials.
That cleared the way for the administration to finalize the release of the assistance. The Defense Department had already begun processing some of those funds, and officials worried that if the White House did not release the funding before the end of the fiscal year on Sept. 30, it would be lost.
Defense and State Department staff members were frustrated when they sought explanations or resolutions from the White House Office of Management and Budget and contacted the offices of members of Congress considered sympathetic to the cause.
Lawmakers pressed the administration on why the Ukraine aid was being held, but were first told the assistance was being reviewed to determine whether it was in the best interest of foreign policy. Other administration officials said, without detail, there was a review on corruption in Ukraine, according to current and former officials. Then, as August drew to a close, other officials told lawmakers they were trying to gauge the effectiveness of the aid, a claim that struck congressional aides as odd, the officials said.
But Vice President Mike Pence later said that the review was based on concerns from the White House about “issues of corruption.” Without detailing those concerns, Mr. Pence, after a meeting with Mr. Zelensky in Warsaw on the sidelines of a commemoration of the outbreak of World War II, told reporters that to invest more taxpayer funds in Ukraine, “the president wants to be assured that those resources are truly making their way to the kind of investments that will contribute to security and stability in Ukraine.”
A handful of Republican and Democratic senators who belong to a bipartisan Ukraine caucus wrote a letter to Mr. Mulvaney early this month expressing “deep concerns” over the delay in releasing the funding. The funding is “vital to the long term viability of the Ukrainian military,” helping it “fend off the Kremlin’s continued onslaughts within its territory,” the senators wrote.
Pressure on the White House from Republican senators intensified. Senator Rob Portman of Ohio spoke to Mr. Trump about the funds, and Senator Lindsey Graham of South Carolina informed the White House that he planned to support an amendment by Senator Richard J. Durbin, Democrat of Illinois, that would block Pentagon spending to ensure that the Ukraine funds were released. On Sept. 11, the administration told lawmakers it would release the funds.
Two days before, Representative Adam B. Schiff, Democrat of California and the chairman of the House Intelligence Committee, had released a letter he had sent to the acting director of national intelligence revealing the existence of a whistle-blower case that might involve the president — touching of a series of disclosures in the news media that brought the controversy over the Ukraine aid to a full crisis.
House Democrats on Monday moved to try to force Mr. Trump’s hand, even as they weighed voting on a resolution this week condemning his actions. At the same time, the chorus of lawmakers demanding impeachment grew louder, underscoring how the latest revelations about the president have touched off a seismic shift under Democrats’ feet.
Seven freshman House Democrats with military and national security experience — most of whom have been reluctant to call for impeachment — spoke out Monday night in a strongly worded opinion article in The Washington Post.
“If these allegations are true, we believe these actions represent an impeachable offense,” the lawmakers wrote.
The authors were Representatives Gil Cisneros of California, Jason Crow of Colorado, Chrissy Houlahan of Pennsylvania, Elaine Luria of Virginia, Mikie Sherrill of New Jersey, Elissa Slotkin of Michigan and Abigail Spanberger of Virginia.
The chairmen of three House committees investigating the matter threatened to issue subpoenas in the coming days if the administration did not hand over a transcript of the call and documents related to the decision to withhold the aid money. A failure to do so — or to disclose to Congress a secretive whistle-blower complaint said to be related to the Ukraine matter — would be considered obstruction, they said, an indication that they could consider it grounds for impeachment.
“If press reports are accurate, such corrupt use of presidential power for the president’s personal political interest — and not for the national interest — is a betrayal of the president’s oath of office and cannot go unchecked,” the chairmen of the House Intelligence, Foreign Affairs, and Oversight and Reform Committees wrote on Monday in a letter to Secretary of State Mike Pompeo.
They added, “By withholding these documents and refusing to engage with the committees, the Trump administration is obstructing Congress’s oversight duty under the Constitution to protect our nation’s democratic process.”
It appeared increasingly likely that the brewing conflict would come to a head on Thursday, when the House Intelligence Committee was already scheduled to question Joseph Maguire, the acting director of national intelligence, who has withheld the whistle-blower complaint under advisement from the Justice Department and the White House. The panel has demanded that Mr. Maguire bring a copy of it with him.
Now, lawmakers also want a decision by Mr. Pompeo — and by extension, Mr. Trump — by that day on whether he will furnish a transcript of the presidential conversation, as well as other materials they have requested.
Mindful that Democrats may have only a brief window to decide their course, Speaker Nancy Pelosi summoned the leaders of six House committees involved in investigations of the president to meet on Tuesday, telling the lawmakers to come without aides. Afterward, she planned to convene a special meeting of the Democratic caucus to discuss impeachment.
Their decisions could have grave implications for Mr. Trump’s presidency.
A growing number of House Democrats said on Monday that the new revelations all but demanded the move. They warned that a decision by the Trump administration not to hand over documents about a matter of urgent national security would leave the House with no choice but to initiate full-bore impeachment proceedings. At the same time, they said, any material that corroborated news reports about Mr. Trump’s actions could lead to the same outcome.
“It is clear that the sitting president of the United States placed his own personal interests above the national security interests of the United States,” said Representative Angie Craig of Minnesota, who flipped a Republican seat last fall. She called for impeachment proceedings to begin “immediately, fairly and impartially.”
Ms. Craig’s announcement came alongside that of another Minnesota freshman, Representative Dean Phillips, who warned, “If the reports are corroborated, we must pursue articles of impeachment and report them to the full House of Representatives for immediate consideration.”
Ms. Slotkin, a former C.I.A. officer who participated in briefings with Presidents George W. Bush and Barack Obama, and who advocated whistle-blower protections while working for Mr. Bush’s director of national intelligence, said the issue was “personal” for her.
“As national security professionals, this was too much,” she said. “While we had always been judicious in thinking about impeachment before, this just crossed a line.”
Other, more veteran lawmakers issued similar statements.
Veteran Democrats close to Ms. Pelosi, who has stubbornly resisted impeachment, joined the chorus as well. “An impeachment inquiry may be the only recourse Congress has if the president is enlisting foreign assistance in the 2020 election,” said Representative Rosa DeLauro of Connecticut. “Congress must meet this pivotal moment in our nation’s history with decisive action.”
There were also indications of more movement to come. Other moderate freshmen who have shied away from impeachment spent the day furiously calling one another in efforts to calibrate their responses. Several said privately that they were on the brink of supporting an impeachment process, but that they wanted to first see what transpired Thursday.
Privately, some Democrats and their aides were more cautious, fretting that the transcript of the July call would not be as damning as billed. They worried that the anticipation of its disclosure was replicating the dynamic that surrounded the release of the report by Robert S. Mueller III, the former special counsel who investigated Russia’s interference in the 2016 elections, in which Democrats had expected a set of clear-cut revelations that would all but demand Mr. Trump’s impeachment, but ended up instead with a document that did not move public opinion against the president.
Democrats got some backup in the Senate from Republicans, who have generally split over whether Mr. Trump is obliged to share either the transcript or the whistle-blower complaint with Congress.
“I believe the most helpful report would be a transcript of the president’s conversation with President Zelensky,” Senator Mitt Romney of Utah, the 2012 Republican nominee for president, told reporters. “That, I think, would be the most instructive. But I certainly believe that the whistle-blower report should also be available to Congress.”
Speaking on the Senate floor on Monday afternoon, Senator Mitch McConnell, Republican of Kentucky and the majority leader, accused Democrats of trying to exploit a serious issue for political gain. He said he had confidence that the Senate’s intelligence panel, working quietly on a bipartisan basis, would handle it appropriately.
Reporting was contributed by Sheryl Gay Stolberg, Catie Edmondson, Emily Cochrane, Jonathan Martin, Peter Baker and Julian E. Barnes.