PHILADELPHIA — A onetime challenger to U.S. Rep. Bob Brady will plead guilty to hiding a $90,000 payment from the powerful Philadelphia Democrat’s campaign in exchange for dropping out of a 2012 primary, his defense lawyer said Thursday.

Former city judge Jimmie Moore met with Brady shortly before exiting the race to discuss the arrangement and it was “agreed and understood” that the payment would be disguised, according to court documents filed by prosecutors Wednesday.

Brady has not been charged with a crime and his lawyer denied there was an agreement to hide the source of the money.

“We don’t think that ever happened,” said attorney James Eisenhower. “We think the congressman has done everything right.”

Moore’s attorney, Jeffrey Miller, said in an interview Thursday that his client stepped down from the bench this week and will admit to a federal charge of filing a false campaign finance report. He said Moore is willing to testify if needed.

“The one thing he won’t waver from is telling the truth,” Miller said, adding that Moore is set to be arraigned in October.

Federal prosecutors said the money was supposed to be used to cover Moore’s large campaign debts, though in a separate filing authorities noted that some of the payment was used for personal expenses.

One of Moore’s campaign aides pleaded guilty in July to concealing the payments on the candidate’s finance reports. That case had been filed under seal after prosecutors argued that Brady had tried to “influence” a witness in the matter. It was unsealed after the aide pleaded guilty.

A guilty plea from Moore could mean that charges against Brady may soon follow, said Adav Noti, a former Federal Election Commission lawyer and the senior director of the nonpartisan Campaign Legal Center.

“The fact that the judge (Moore) is pleading,” Noti said, “it suggests that a charge against Brady is coming.”

Brady has run the Democratic Party machine in Philadelphia for three decades. He entered Congress in 1998.