WASHINGTON — President Trump’s former national security adviser, Michael T. Flynn, pleaded guilty on Friday to lying to the F.B.I. about conversations with the Russian ambassador last December, becoming the first senior White House official to pledge cooperation in the special counsel’s wide-ranging inquiry of election meddling.
Documents released as part of Mr. Flynn’s plea agreement show that his pre-inauguration discussions with Sergey I. Kislyak, the Russian ambassador, about foreign policy were part of a coordinated effort by aides running Mr. Trump’s transition into the White House. In at least one instance, federal prosecutors say, Mr. Flynn was directed by a “very senior member” of Mr. Trump’s presidential transition team.
Court documents do not name the official or disclose what Mr. Trump knew about Mr. Flynn’s discussions. The transition team was led by Vice President Mike Pence, and its top aides included Jared Kushner, the president’s son-in-law and adviser; Reince Priebus, Mr. Trump’s first chief of staff; and K.T. McFarland, who was Mr. Flynn’s deputy and is now the ambassador to Singapore.
Mr. Flynn’s decision to plead guilty marked a significant new phase in the investigation of the special counsel, Robert S. Mueller III, and a politically treacherous development for the president and his closest aides, whose activities in the West Wing are being scrutinized by F.B.I. agents and federal prosecutors.
Mr. Flynn’s admissions in his plea deal could deeply undercut the arguments made in January by Mr. Trump and his aides that they were not fully aware of Mr. Flynn’s discussion with Russians about sanctions imposed on Russia by the Obama administration over the election meddling. In fact, the documents say multiple members of the team coordinated the specifics of Mr. Flynn’s outreach to Russia and knew that the conversations were about sanctions.
Court documents say that on Dec. 29, Mr. Flynn called a senior transition official who was with other members of the team at Mr. Trump’s Mar-a-Lago club in Florida “to discuss what, if anything, to communicate to the Russian ambassador about the U.S. sanctions.”
In a statement issued after he entered his plea in a federal courthouse in Washington, Mr. Flynn, 58, denied “false accusations of ‘treason,’” but said that he had agreed to cooperate with federal prosecutors, who are examining whether Mr. Trump’s campaign colluded with Russians during the election and whether the president or his aides sought to cover up those efforts.
“I recognize that the actions I acknowledged in court today were wrong, and, through my faith in God, I am working to set things right,” Mr. Flynn said. “My guilty plea and agreement to cooperate with the special counsel’s office reflect a decision I made in the best interests of my family and of our country. I accept full responsibility for my actions.”
During the court hearing, prosecutors focused on Mr. Flynn’s activities during the transition, when he discussed with Mr. Kislyak the sanctions, and later talked with Russia and other countries about their votes on an upcoming United Nations resolution.
Prosecutors did not disclose at the hearing any new details about Russia’s interference in the 2016 presidential election or whether any of Mr. Trump’s associates were involved.
Ty Cobb, the president’s lawyer dealing with the Russia inquiry, played down the potential impact of Mr. Flynn’s deal with federal authorities, saying that Mr. Flynn served only briefly in the administration and had pleaded guilty to a single count of lying to the F.B.I.
”Nothing about the guilty plea or the charge implicates anyone other than Mr. Flynn,” Mr. Cobb said in a statement, repeating the White House hopes that Mr. Mueller will conclude the investigation quickly.
While Mr. Trump can point to the court documents and say they show no evidence of collusion with Russia, the special counsel’s filings so far paint a damning portrait of Mr. Trump’s associates. His former campaign chairman, two other campaign aides, and his former national security adviser have now all been charged with felonies.
The 45-minute hearing marked a humiliating moment for Mr. Flynn, a decorated Army general who had risen to lead the Defense Intelligence Agency but was fired by former President Barack Obama before joining the Trump campaign. Mr. Flynn was an early supporter of Mr. Trump, who tapped him to become the national security adviser, a prestigious and influential post.
Mr. Flynn, dressed in a crisp gray suit, arrived at the courtroom with his wife, holding hands. They occasionally traded glances, and his wife’s legs trembled before prosecutors laid out their case that Mr. Flynn had repeatedly lied to investigators about his dealings with Russia and his lobbying on behalf of the Turkish government.
Mr. Flynn’s plea agreement requires his full cooperation. He agreed to provide prosecutors information on “any and all matters” they request. He agreed to take a polygraph and, if asked to, participate in covert law enforcement activities. Such undercover activities are unlikely, however, since the plea agreement was filed publicly.
Prosecutors said they would delay Mr. Flynn’s sentencing, a sign that their investigation was not over and that they had not exhausted Mr. Flynn’s cooperation. Lying to the F.B.I. carries a penalty of up to five years in prison. Mr. Flynn left the courtroom and was told to check in weekly with federal authorities.
Mr. Flynn’s cooperation could be valuable to guide Mr. Mueller’s understanding of the campaign’s contacts with Russia, even if he cannot directly implicate anyone in a crime. Since he pleaded guilty to lying, Mr. Flynn hurt his credibility as a witness if he ever offered evidence against someone else at trial.
According to prosecutors, he discussed with Mr. Kislyak an upcoming United Nations Security Council vote on whether to condemn Israel’s building of settlements. At the time, the Obama administration was preparing to allow a Security Council vote on the matter.
Mr. Mueller’s investigators have learned through witnesses and documents that Prime Minister Benjamin Netanyahu of Israel asked the Trump transition team to lobby other countries to help Israel, according to two people briefed on the inquiry. Investigators have learned that Mr. Flynn and Mr. Kushner took the lead in those efforts. Mr. Mueller’s team has emails that show Mr. Flynn saying he would work to kill the vote, the people briefed on the matter said.
In the other discussion, according to court documents, Mr. Flynn asked Mr. Kislyak that Moscow refrain from escalating the situation in response to sanctions announced by the Obama administration that day against Russia over its interference in the presidential election. And Mr. Kislyak told Mr. Flynn that Russia “had chosen to moderate its response,” the documents said.
The following day, President Vladimir V. Putin of Russia said Moscow would not retaliate against the United States in response to the sanctions.
Mr. Trump praised the Russian leader in a Twitter post at the time.
Great move on delay (by V. Putin) – I always knew he was very smart!
— Donald J. Trump (@realDonaldTrump) December 30, 2016
But American intelligence agencies had grown so concerned about Mr. Flynn’s communications with Mr. Kislyak and false accounts that he provided to Vice President Mike Pence that he was interviewed by F.B.I. agents at the White House four days after the president was sworn into office, and the acting attorney general, Sally Q. Yates, warned the White House that its national security adviser might be compromised by the Russians.
Mr. Flynn served just 24 days, resigning on Feb. 13 after it was revealed that he had misled Mr. Pence and other top White House officials about his conversations with Mr. Kislyak.
But after accepting Mr. Flynn’s resignation, the president repeatedly said he thought Mr. Flynn was “a very good person” who had been treated poorly. The day after Mr. Flynn quit, Mr. Trump told the F.B.I. director at the time, James B. Comey, “I hope you can see your way clear to letting this go, to letting Flynn go,” according to a memo Mr. Comey wrote describing that meeting.
In a news conference two days after Mr. Flynn’s resignation, the president blamed the media.
“General Flynn is a wonderful man,” Mr. Trump said. “I think he has been treated very, very unfairly by the media, as I call it, the fake media in many cases. And I think it is really a sad thing that he was treated so badly.”
During the campaign, Mr. Trump repeatedly castigated Hillary Clinton for what he asserted were lies that she made to the federal authorities as secretary of state.
“Crooked Hillary Clinton lied to the F.B.I. and to the people of our country,” Mr. Trump said in a Twitter post in July 2016. “She is sooooo guilty. But watch, her time will come!”
Even before Mr. Trump said he would appoint Mr. Flynn as his national security adviser, questions swirled around Mr. Flynn’s connections to Russia, particularly a dinner he was paid to attend in Moscow in 2015 when he sat at the same table as Mr. Putin.
Throughout the campaign, Mr. Flynn was an intense and vocal advocate of closer relations with Mr. Putin, arguing that the United States must work with the Russians to battle extremists. After he was named national security adviser, he continued to urge closer cooperation between the two nations.
Mr. Flynn was a prominent member of Mr. Trump’s campaign, often appearing on Fox News to advocate the candidate’s foreign policy views.
Like Mr. Trump, Mr. Flynn was a brash, outspoken critic of Mr. Obama, asserting that Shariah, or Islamic law, was spreading in the United States — a claim that was repeatedly debunked — and saying that the United States was in a “world war” with Islamist militants.
After he left the Obama administration, Mr. Flynn formed a consulting group that led to inquiries into questionable lobbying for foreign governments, including the Turkish government, and hazy business ties with Middle Eastern countries.
Investigators working for the special counsel have questioned witnesses about Mr. Flynn’s dealings with the Turkish government and whether he was secretly paid by Turkish officials during the campaign. After he left the White House, Mr. Flynn disclosed that the Turkish government had paid him more than $500,000 to represent its interests in a dispute with the United States.
Prosecutors did not charge Mr. Flynn on Friday with crimes related to his work with the Turkish government. But in documents released after the hearing, they made clear that they have evidence that Mr. Flynn “made materially false statements and omissions” in his federal filings about that lobbying work.
White House officials had been bracing for troublesome developments in the special counsel investigation, even as the president and some of his senior advisers had been saying in recent weeks that they believed Mr. Mueller was nearing the end of his inquiry.
Mr. Trump was not scheduled to make any public comments on Friday, though Mr. Flynn’s plea provided an awkward backdrop for remarks he was scheduled to give behind closed doors at an afternoon holiday reception with members of the news media.
But earlier this year, Mr. Trump offered Mr. Flynn legal advice in a Twitter post: “Mike Flynn should ask for immunity in that this is a witch hunt (excuse for big election loss), by media & Dems, of historic proportion!”