Less than a week after he officially got in, former Lt. Gov. Mark Singel has dropped out of the race for U.S. Rep. John P. Murtha's seat.

Mr. Singel cited a need for the Democratic Party to unify as a reason for departing, leaving as the clear favorite Mr. Murtha's former district director, Mark Critz, who earned the endorsement of Mr. Murtha's widow, Joyce, Thursday.

Mr. Murtha died Feb. 8 of complications related to gall bladder surgery.

"If we're going to sustain a candidate in a tough race, it behooves us to get behind that person sooner rather than later," Mr. Singel said. "And I mean even before state committee leaders meet and pass judgment."

Democratic leaders from the 12th District will meet March 6 to select a candidate to submit to the state committee for the May 18 special election.

Mr. Critz announced his endorsement from Mrs. Murtha in the wee early hours Thursday. Later in the day, Westmoreland County Commissioner Tom Ceraso and Mr. Singel, of Johnstown, left the race. The remaining declared Democrats include former state treasurer and auditor general Barbara Hafer, Navy veteran Ryan Bucchianeri, former Johnstown reporter Ron Mackell Jr. and Cambria County controller Ed Cernic Jr.

But Mr. Singel said Mrs. Murtha's endorsement of a rival did not affect his decision -- and he did not immediately offer his backing to any of the remaining candidates.

Mr. Singel said he will not seek the seat in November, either.

Republican conferees will meet March 11 at Saint Vincent College in Latrobe to select their candidate.

Retired Army Lt. Col. William Russell, who lost to Mr. Murtha in 2008, and Eighty Four businessman Tim Burns are competing for the GOP nod.

Scottdale physician Bruce Teich has filed to run as an independent.

Washington correspondent Daniel Malloy writes the "Pittsburgh On The Potomac" blog exclusively at PG+, a members-only web site of the Pittsburgh Post-Gazette. Our introduction to PG+ gives you all the details.