WASHINGTON — The F.B.I. is investigating whether Representative Robert A. Brady of Pennsylvania, the top Democrat on the House Administration Committee, illegally paid a political opponent $90,000 to drop out of a 2012 primary race, court documents show.

Two of Mr. Brady’s political consultants have already been charged in a campaign finance investigation of the congressman’s 2012 re-election. But a recently unsealed application for a search warrant suggests Mr. Brady may be a target of the inquiry.

The allegations involve payments the Brady campaign made to the campaign of Jimmie Moore, a former Municipal Court judge in Philadelphia who ended his run for Congress in February 2012.

In the search warrant application, the F.B.I. said the payments were disguised as reimbursement for a poll and funneled through shell companies created by Mr. Brady’s aides “for the sole purpose of using money from the Brady campaign to repay Moore campaign debts.”