Rep. Roscoe G. Bartlett’s top aide has resigned in the wake of reports he was lining up support to run for the Maryland Republican’s seat in 2012.

Bud Otis, Bartlett’s longtime chief of staff, has been soliciting endorsements in case Bartlett decides not to seek an 11th term in the 6th Congressional District, which has been altered under the state’s new redistricting map to include a portion of Democratic-leaning Montgomery County.

Otis has indicated he is planning to run only if Bartlett, 85, does not, and the incumbent has vowed to seek reelection. But some Republicans have been skeptical of that pledge. On Thursday, state GOP Chairman Alex X. Mooney, a former state senator who once worked for Bartlett, said he would explore a bid for the seat. State Sen. David R. Brinkley (Frederick) also announced that he was starting an exploratory committee.

Bartlett spokeswoman Lisa Wright said Bartlett accepted Otis’s resignation Wednesday night because “the multiple recent news reports about Bud’s activities made it impossible for Bud to continue to serve him and the residents of the 6th District of Maryland effectively.”

On the Democratic side, Lt. Gov. Anthony G. Brown said Thursday that he was backing state Sen. Robert J. Garagiola (Montgomery) in the contest. The seat was drawn by Annapolis Democrats with Garagiola in mind, but former Montgomery County Council member Duchy Trachtenberg and financier John K. Delaney are also running for the nomination.

Rep. Roscoe Bartlett (R-Md.) wraps up a staff meeting before a briefing for the House Armed Services Committee in January. Bartlett lost his chief of staff Dec. 1 after rumors surfaced that Bud Otis would run against his boss. (Melina Mara/THE WASHINGTON POST)