(Adds details on property, forfeiture request)

By David Shepardson

WASHINGTON, Nov 4 (Reuters) - President Donald Trump's former campaign manager Paul Manafort offered to post more than $12 million in real estate and life insurance assets and to limit his travel in a bid to avoid continued house arrest, according to court documents filed on Saturday.

Manafort, who ran Trump's presidential campaign for several months last year, and associate Richard Gates earlier this week pleaded not guilty to a 12-count indictment by a federal grand jury.

The charges include conspiracy to launder money, conspiracy against the United States and failing to register as foreign agents of Ukraine’s former pro-Russian government. They are part of Special Counsel Robert Mueller's investigation into alleged Russian efforts to tilt the 2016 election in Trump's favor and potential collusion by Trump associates.

In the Saturday court filing, Manafort offered to limit his travel to New York, Washington and Florida and pledged life insurance worth about $4.5 million as well as about $8 million in real estate assets, including a property on Fifth Avenue in New York that was identified by some media outlets as an apartment in Trump Tower.

U.S. District Judge Amy Berman Jackson said on Thursday that initial bail terms would remain in place and set a bail hearing for Monday to consider changes. On Friday, she suggested a potential May 7 trial date.

Manafort and Gates are under house arrest, under unsecured bonds of $10 million and $5 million, respectively, which means they do not have to post the bail unless they fail to show up for court or violate other conditions.

Prosecutors have argued there is a risk of flight and both men are subject to electronic monitoring.

As part of the indictment, the special counsel's office is seeking forfeiture of four of Manafort's properties in connection with money laundering charges.

Peter Carr, a spokesman for Mueller, declined to comment on Saturday.

Manafort, 68, in the filing also explained why he had three different U.S. passports, a fact noted by prosecutors. Manafort's lawyer, Kevin Downing, rejected suggestions that Manafort was a "Jason Bourne character" - referencing a fictitious, globe-trotting, rogue covert agent.

"The facts are much more mundane," Downing wrote.

Manafort had two passports, including one for submitting to foreign governments to receive visas while traveling on the other, his lawyers said. He was issued a third passport because one had been lost and Manafort contacted passport services to advise them it was found.