When Seth Williams tomorrow becomes the first candidate to launch a campaign to become Philadelphia's next district attorney, he will push for many of the same changes he did when he sought the job in 2005.

He plans to call for restructuring the office so that assistant prosecutors would be assigned to neighborhoods citywide, instead of specific courtrooms that hear cases at random. And he will propose a new program to focus on nonviolent offenders as a way to deter crime.

Despite those similarities, however, the race Williams is getting into this time will be markedly different.

With District Attorney Lynne M. Abraham retiring from office, there will be no incumbent on the ballot for the first time since 1985.

As a result, the race is wide open, with about half a dozen mostly Democratic candidates said so far to be interested in competing in the May primary election.

"What you are going to see is a number of folks position themselves to be the front-runner. No one has really taken that position as of yet," Democratic political consultant Maurice Floyd said.

"I expect it to be very competitive," he added, "but I think it will boil down to who can raise the finances to compete, to put together the right team, to orchestrate the message that they are going to be the next D.A."

Other than mayor, the position is perhaps one of the most powerful and influential in the city, with far-reaching implications on Philadelphia's most oft-pressing problem: crime.

The job has never been held by an African American, though Williams and at least two other potential candidates are working to change that.

The position has served frequently as a springboard to higher office. U.S. Sen. Arlen Specter, Gov. Rendell, and Ronald Castille, chief justice of the Pennsylvania Supreme Court, each served as district attorney.

"It's going to be hand-to-hand combat, figuratively, with everybody trying to scrounge up as many votes as they can," said former City Councilman Daniel McElhatton, who also plans to run for the seat.

McElhatton has formed a political committee and intends to declare his candidacy early next year - much like two others, Dan McCaffery and Michael L. Turner.

"It's going to be a very spirited campaign," said McCaffery, brother of state Supreme Court Justice Seamus McCaffery and a lawyer with Friedman Schuman.

"It's going to be a tough race," said Turner, a lawyer at Marshall, Dennehey, Warner, Coleman & Goggin. "It's not a situation where you have one person running against an incumbent. It's an open field."

Resumes for nearly everyone interested in the position include stints - some shorter, some longer - as an assistant district attorney in Philadelphia.

Other potential candidates include Brian Grady, now at the firm of Brady & Falcione; former city solicitor Kenneth Trujillo; and Common Pleas Court Judge Leon Tucker, who would have to resign from the bench to run.

Williams tomorrow is set to become the first to officially declare his candidacy, in an 11 a.m. speech he plans to deliver at the National Constitution Center.

"My mantra is we have to be smart on crime, not just tough," Williams, who is in private practice at Stradley, Ronon, Stevens & Young, said in an interview yesterday.

Besides laying out detailed proposals, Williams said he would also announce that he has hired as a senior policy adviser Lawrence Sherman, a University of Pennsylvania criminologist.

Williams, 41, spent more than 10 years as assistant district attorney, heading up the repeat-offenders unit and the Municipal Court unit. He left in mid-2003, about the same time he began his Democratic primary battle against Abraham. He lost that bid, getting 46 percent of the vote, to Abraham's 56 percent.

In 2005, Mayor John F. Street hired Williams as his inspector general, a position he held until early this year. What he learned in that post - dealing with government bureaucracy, management skills, media relations - "will make me an even better district attorney than I would have been in 2005," he said.

Contact staff writer Marcia Gelbart at 215-854-2338 or mgelbart@phillynews.com.