Former Bucks County Congressman Patrick Murphy is running for office again, this time for Pennsylvania attorney general.

The 37-year-old Democrat, who lost his seat in October to Republican U.S. Rep. Mike Fitzpatrick, touted his military record and vowed to keep fighting for Pennsylvanians should he be elected the state's top prosecutor in 2012.

"The people of Pennsylvania need someone in the attorney general's office that's going to stand up for them and protect them from criminals on the street and big special interests that prey on the vulnerable," he said.

Murphy made his announcement Wednesday with a speech in the Fairmount section of Philadelphia, and released a list of more than 40 endorsements from various unions and Democratic leaders, including U.S. Rep. Chaka Fattah (D., Phila.), former gubernatorial nominee Dan Onorato, and the chairmen of Bucks and Montgomery counties' Democratic Parties.

The ex-congressman's entry into the race makes him the second Democrat to officially declare candidacy in what is already a growing 2012 field.

Last month, Kathleen Granahan Kane, a former prosecutor from Scranton, announced she would run for the office. Former Philadelphia District Attorney Lynne M. Abraham and Dan McCaffery, who finished second to Seth Williams in Philadelphia's 2009 district attorney race, have also expressed interest.

They may face tough odds, though. No Democrat has held the state attorney general's office since it became an elected post in 1980.

At this point, the Republican side remains murky. Since Gov. Corbett left the office for the governor's mansion, the attorney general's seat has been held by Bill Ryan, a top deputy in that office.

Corbett has nominated federal prosecutor Linda Kelly of Pittsburgh to serve out the rest of his term, but she awaits Senate confirmation. In accepting the nomination, she said she would not run for a full four-year term in 2012.

Murphy said there needed to be a stronger watchdog for Pennsylvanians against special interests. He tipped his hat to Corbett, though, for his emphasis on corruption prosecutions.

"People in Pennsylvania are tired of elected officials feathering their own nest," Murphy said. "For me, public corruption should be an even higher priority."

An Iraq war veteran, Murphy has worked as a military prosecutor, constitutional law professor at West Point, and special assistant U.S. attorney for the Southern District of New York.

He was elected to Congress in a narrow victory over then-incumbent Fitzpatrick in 2006 - only to be booted out last year as the GOP's midterm high tide swept Fitzpatrick back into his seat.

Since January, Murphy has split time teaching at Widener Law School's Harrisburg branch and working at the Philadelphia law firm Fox Rothschild.

"I think some people thought there would be a 'round three' in the Irish donnybrook in Bucks County," he joked of his races against Fitzpatrick. "But this is the next chapter in my public service."

Contact staff writer Jeremy Roebuck at 267-564-5218 or at jroebuck@phillynews.com.