Pittsburgh Mayor Luke Ravenstahl said yesterday that he accepted a letter of resignation and application for retirement from Police Chief Dominic J. Costa, and was launching a fast-track process to name a new chief.

He named Assistant Chief Paul Donaldson as acting chief, and said that assistant chiefs Nate Harper and Earl Woodyard and Director of Operations Regina McDonald also would be among the candidates for the job. Interviews for the $92,285-a-year position start next week.

The mayor's announcement late yesterday afternoon ended 24 hours of uncertainty about the chief's status, after an administration spokesman and the chief's wife both said that he had not resigned.

The mayor said he only became aware last week of the chief's worsening medical condition from a 2002 gunshot wound that left a bullet in his brain stem.

"When we had our first sit-down meeting he brought it to my attention that he wasn't feeling well and that this indeed may have to happen," the mayor said. "The medical consequences from his gunshot wound of 2002 led him to this decision that he made, and we agreed that it would be best for him to retire."

"It doesn't look good, let's put it that way,'' a haggard-looking Mr. Costa, 55, said yesterday when he exited his Stanton Heights home dressed in matching light blue shirt and pants. "I can't do it anymore -- the pain, I'm losing weight, I just can't do it anymore.

"I've got numbness in my hands. I guess if I were younger, it would have helped."

He said he sent his retirement papers to the city pension office mid-day yesterday and then took a nap to relieve the crushing pain from the bullet.

The mayor said he understood the chief had been suffering for several months, but did not want to bring attention to it during the late Mayor Bob O'Connor's battle with brain cancer.

Both Mr. Ravenstahl and Mr. Costa denied that the chief had been urged to resign by the mayor or staff.

"I know there's speculation out there, but there's no truth to that," Mr. Ravenstahl said.

"He and I had had a discussion on the direction the bureau was going," he said. He asked the chief to reconsider disbanding the aggressive Impact Squad, and the chief obliged, reversing that decision.

"He worked well with me and with my staff," the mayor said.

"We've gotten along well, so far," Mr. Costa said of the mayor.

City Director of Operations Dennis Regan supervised Mr. Costa after the July 27 firing of then-Chief of Staff B.J. Leber.

Mr. Regan said he "didn't have a chance to evaluate" the chief's performance, though he confirmed that he spent time visiting zone stations and checking to see how the bureau was operating.

Mr. Costa was shot during a February 2002 standoff with an armed fugitive in Homewood.

He was severely criticized for his actions in that incident on Hermitage Street in a confidential 52-page report that was obtained in January by the Pittsburgh Post-Gazette. The incident ended in the shooting of Officer Thomas Huerbin, fugitive Cecil Brookins and Mr. Costa.

The report criticized Mr. Costa for usurping too much authority and violating protocols. Then-Chief Robert W. McNeilly Jr. recommended a 10-day suspension and retraining, but Mr. Costa did not return to work with the city after he was wounded.

When Mr. Costa returned to be police chief under Mr. O'Connor, then city Solicitor Susan Malie said the disciplinary recommendation had expired and the suspension and retraining would not be required.

Though both Mr. Ravenstahl and the chief attributed the retirement to the medical condition, longtime Costa friend and former Police Chief Ralph Pampena said he believes the mayor likely wanted to appoint his own person to the position.

"You know, I think it's a shame that when there's a change in the political structure the chief has to go," he said.

Mr. Pampena, who was eased out of the chief's position after the 1988 death of Mayor Richard Caliguiri, said he had spoken with Mr. Costa a month ago.

"I'm sorry to see him go. He's been very, very good to the Pittsburgh police officer," said Fraternal Order of Police President Jim Malloy. He said Mr. Costa had been complaining of sleeplessness, numbness and pain, but added that Mr. Ravenstahl's Sept. 1 ascent may have contributed to the timing.

During a 25-year career with the Pittsburgh police, Mr. Costa had been on leave for a total of six years and collected $410,000 in workers' compensation.

The chief received $298,000 in compensation as a result of the Homewood shooting. He began receiving payments five days after he was shot.

He stopped receiving compensation in June 2005, when he began a job as the Penn Hills public safety director. He left that to join the O'Connor administration in March.

Neither the mayor nor spokesman Dick Skrinjar could say whether the chief's retirement would be processed as a normal pension or a disability pension. Mr. Malloy said that would impact both the amount and the duration of the benefits.