PITTSBURGH - Sen. Arlen Specter said yesterday that he was "pleased and proud" to return to his roots as a Democrat, invoking FDR and JFK as inspirations during a speech to the leaders of the state party.

"We share core beliefs, beliefs I have advanced and defended for decades, even when my party was against me, even when it might cost me an election," said Specter, a five-term incumbent who switched parties six weeks ago after Republicans revolted against him for providing a crucial vote for President Obama's economic stimulus.

"The far right used me for target practice, and they didn't like it when I wouldn't stand still," Specter said in a 17-minute speech that was interrupted by applause 20 times. "So I'm especially glad to be here with you, where I feel so welcome."

He talked about the stimulus vote and recited a litany of other stances he had taken that jibed with Democratic policy, including raising the minimum wage, protecting abortion rights, expanding access to health care, funding stem-cell research, and fighting global warming.

Specter, acknowledging that his maiden party speech as a Democratic senator was important to him, used a teleprompter for the first time in years because he wanted to "express myself with precision" to the 194 members of the Democratic State Committee convening for their annual spring meeting at the Westin Convention Center Hotel.

He received five standing ovations, capping off two days of politicking. On Friday night, during a celebration of the late Lt. Gov. Catherine Baker Knoll, Gov. Rendell told Democrats that Specter's vote for the stimulus package had "saved the country."

Specter was received warmly by most, though warily by a few, of the Democratic activists in attendance at the series of workshops, caucuses, and the Knoll dinner. U.S. Rep. Joe Sestak of Delaware County, who is likely to challenge Specter for the Democratic Senate nomination in 2010, also made the rounds, though he did not address the committee.

"Only an act of God" could keep him from running, Sestak told a committee member.

Rendell said it would be tragic if Sestak runs because he would lose to Specter and the Democrats might not be able to hold onto the congressional seat.

"This is not a place for kingmakers," Sestak, 57, a former Navy vice admiral, told reporters who asked him about Rendell's comments.

After Specter's speech yesterday, several Democrats said they would wait to see how he votes in coming months.

"I welcome all evolution in thinking," said Mary Ann Weaver, a state committeewoman from Lawrence County. "He was a Republican for a long time," she said, adding that she thought Specter had done a lot of good on health-care issues.

"I spent two or three elections of my life trying to knock this guy out. In 2004, we went from county to county, saying he was the Antichrist," said Philadelphia operative D.A. Jones. "Now, he's on our team. It's hard to wrap my head around."

Noting the independence that got him in hot water with his former party, Specter said he was sure some of his listeners would disagree with him at times. But he vowed to "make you proud."

Before the speech, Specter told a raucous labor rally outside the hotel he was "committed to finding an answer" that would result in passage of the Employee Free Choice Act, a bill stalled in the Senate that would make unionizing easier.

As a Republican, Specter said in March that he would not vote to cut off debate on the bill because of the so-called card-check provision that would allow unions to be certified by workers' signatures without a secret ballot. Business groups say the legislation would open workers to union intimidation.

Since then, Specter has soft-pedaled his opposition and is part of a key group of moderate senators working on a compromise designed to preserve the secret-ballot aspect of union elections while removing procedural impediments that employers have used to defeat or stall unionization.

"You want my vote? I want yours," retired ironworker John Heinlein of Pittsburgh yelled repeatedly until Specter was forced to acknowledge him.

"I understand that your job's on the line and my job's on the line," Specter said. "I understand that and I believe you'll be satisfied with my vote on this issue."

Specter spoke of other times he had supported organized labor's position and said he understood the depths of their concerns.

"If you want to be elected in this state, you have to come to labor," he said. "I know that."

Contact staff writer Thomas Fitzgerald at 215-854-2718 or tfitzgerald@phillynews.com.