(Updates with more background and details from the hearing)

By Sarah N. Lynch

WASHINGTON, Dec 17 (Reuters) - A federal judge sentenced U.S. President Donald Trump's former deputy campaign chairman Rick Gates to serve an intermittent term of 45 days in jail and 36 months of probation, saying that while she was moved by his extensive cooperation with prosecutors, she still felt some punishment was in order.

U.S. District Judge Amy Berman Jackson said she had struggled for some time with how to sentence Gates, who met with investigators more than 50 times and helped the government secure convictions of Republican operatives Paul Manafort and Roger Stone after he pleaded guilty in February 2018 to lying to the FBI and the special counsel's office and conspiring against the United States.

Jackson said that everyday she sees people who commit crimes "of a much more limited scope" than Gates' offenses who are motivated by drug addictions and poverty, and who then, like Gates, become government witnesses by turning on their own friends and neighbors.

"Even they often serve some time," Jackson noted.

Gates, who held senior posts on the president's campaign team and inauguration committee, was one of several former Trump aides and advisers to be charged in Mueller's investigation that documented Russian interference in the 2016 U.S. election. Gates, 47, initially pleaded not guilty but reversed himself in February 2018 and agreed to cooperate with prosecutors.

Jackson also said he will be required to pay a $20,000 fine, complete community service and continue cooperating in several still-ongoing investigations.

The judge gave Gates leeway to work with the probation office to iron out the terms of when he will serve his 45 days in jail, saying he could do so on weekends or during times that will not interfere with his parenting responsibilities or his ongoing cooperation with law enforcement.

"I wish to express to this court that I accept complete responsibility for my actions that have led me here," Gates said before the sentence was imposed.

"I greatly regret the mistakes I have made and I have worked hard to honor my commitment to make amends. My family and I appreciate your consideration for leniency, and I hope and pray that you will give that to me."

Under the sentencing guidelines calculated by the government, he could have faced up to 4-3/4 years in prison.

Gates' defense attorney Thomas Green had tried to persuade Jackson to sentence his client to probation, and prosecutors did not push back on that recommendation.

Before the start of Tuesday's sentencing hearing, one of the former lead prosecutors in the case, Andrew Weissmann, showed up in court and made a point of shaking Gates' hand.

Green said he saw a number of investigators whom Gates had cooperated with at the courtroom, and they were not just there out of curiosity.

"I am quite certain they are here to acknowledge the genuine contributions that Mr. Gates made to their continuing investigations," he told the judge.

Gates appeared as a star witness for the prosecution in three trials.

He testified against Manafort, his former business partner and mentor, who was convicted in Virginia of financial fraud in August 2018 and is now serving a 7-1/2-year prison sentence. Manafort served as Trump's campaign chairman.

Last month, Gates testified against Stone, Trump's longtime adviser who was convicted by a jury in November in Washington of lying to Congress, obstruction and witness tampering. His sentencing, also by Jackson, is set for February.

Gates also testified against Greg Craig, who served as White House counsel under Democratic former President Barack Obama and was acquitted in Washington in September of lying to authorities about work he performed for Ukraine..

Gates and Manafort were among the first people in Trump's inner circle to face charges by Mueller, who was appointed in May 2017. The charges to which Gates pleaded guilty related to tax fraud, concealing foreign bank accounts and violating the Foreign Agents Registration Act regarding work done for Ukraine's former pro-Russia government.

Until his decision to cooperate, Gates faced more serious charges, which also included helping Manafort file false tax returns, subscribing to false tax returns about his own income and lying about the existence of overseas accounts.

Jackson said she believed that Gates was sincere and appeared to be a very credible government witness who "didn't come across as some sort of bought-and-paid-for puppet" for the government.

Nevertheless, she said, he was "hardly a minor player" in the fraud, and she rejected the notion that he somehow got swept into the drama of Washington politics.

"Politics don't corrupt people. People corrupt politics," she said.

(Reporting by Sarah N. Lynch; Editing by Will Dunham and Jonathan Oatis)

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