Meehan's successor will be First Assistant U.S. Attorney Laurie Magid. She will become the first woman to head the powerful office, which brings criminal and civil actions on behalf of the federal government in the nine-county eastern part of the state.

At a news conference, Meehan, 52, a Republican from Delaware County, sidestepped questions about political ambitions, saying that if an "opportunity for public service is there at some point in time, I will consider that."

Several Republican leaders agreed, however, that Meehan was serious about running for governor, and they said leaving the Justice Department frees him up to begin laying the political groundwork for such a campaign.

"He has an ideal profile for that position," said Shanin Specter, a lawyer and GOP strategist, who said that running for governor would be a "natural progression" for Meehan.

"Many prosecutors have advanced to important statewide office, both in Pennsylvania and elsewhere," said Specter, whose father, U.S. Sen. Arlen Specter (R., Pa.), was once Philadelphia's district attorney.

Meehan is expected to campaign as a statewide surrogate for the GOP presidential candidate, Arizona Sen. John McCain, and to begin raising money after the November general election, party sources said.

Meehan's decision comes in the final six months of the Bush administration, and as several would-be candidates for governor in both parties are raising money and taking steps to explore the 2010 race.

Meehan, a former aide to Arlen Specter, was Delaware County district attorney until President Bush appointed him U.S. attorney in 2001. He is considered a potentially formidable candidate as the GOP searches for a standard bearer with enough stature to take back the governor's office after two terms of Democratic rule.

Mayor Nutter, who hired three former prosecutors from Meehan's office to help rub out City Hall corruption, said the federal investigation of city government "helped restore legitimacy and credibility" to Philadelphia government.

"He has been a true presence and force but also a person with great credibility," Nutter, a Democrat, said of Meehan.

Not only does Meehan have a law enforcement background attractive to voters, but he also has practical political experience from having run two statewide campaigns, for Specter and former Sen. Rick Santorum (R., Pa.).

Meehan also would be running from a geographic base in Southeastern Pennsylvania, where Republicans must poll well to win statewide elections.

"A lot of people think Pat would make an excellent candidate," said Charles G. Kopp, a Center City lawyer and prominent Republican fund-raiser.

Former U.S. Rep. Pat Toomey, of the Lehigh Valley, has told fellow Republicans he is seriously considering a campaign for governor.

Pennsylvania Attorney General Tom Corbett, who is running for reelection this fall, also has been mentioned prominently as a possible GOP gubernatorial candidate.

Several Democrats already have been raising money and exploring 2010 candidacies: Lehigh County Executive Don Cunningham; Allegheny County Executive Dan Onorato; and Philadelphia businessman Tom Knox, who ran for mayor last year.

During Meehan's tenure as U.S. attorney, prosecutors in his office won convictions in several corruption cases, including those involving former City Treasurer Corey Kemp, who is serving a 10-year prison term, and ex-City Councilman Rick Mariano, who was sentenced to seven years behind bars.

"Our work in this area is not done, and it will continue beyond my tenure," Meehan told reporters.

U.S. attorneys traditionally serve at the pleasure of the president, and if Barack Obama wins in November, he would likely appoint a Democrat to succeed Meehan.

The senior Specter said in a statement that it was "understandable" that Meehan would be stepping down.

"Pat Meehan has done an excellent job as U.S. attorney. He has established himself as one of the best in a long line of distinguished lawyers who have held that important position. Considering the fact that the president's term is coming to an end, it is understandable that he is looking to a career change," Pennsylvania's senior senator said.

Meehan's exodus is not expected to have a major impact on the direction of the U.S. Attorney's Office, where the top priorities remain prosecuting public corruption, taking on health-care fraud, and combatting street violence with tough federal weapons charges.

The forthcoming trial of State Sen. Vincent J. Fumo is scheduled to remain on track to start in September.

Magid, 47, a Republican who was an assistant district attorney in Philadelphia and Delaware County before joining the U.S. Attorney's Office in 2001, said she intended to continue the priorities of Meehan's tenure.

"He's going to be a tough act to follow, but I am looking forward to it," said Magid, who will become acting U.S. attorney and serve at least until a new president is elected.

Inquirer staff writer Jeff Shields contributed to this article.