PITTSBURGH - A preview of next year's Pennsylvania Democratic Senate primary played out in a hangar-size convention hall yesterday, as Sen. Arlen Specter and Rep. Joe Sestak took turns wooing attendees at Netroots Nation, the annual national conference of liberal bloggers and activists.

Specter, the recent party convert, carried the heavier burden of skepticism going into the moderated question-and-answer session at the David Lawrence Convention Center, but he argued that he had consistently supported core Democratic principles - and was fresh from three days of harsh town meetings defending President Obama's plans to overhaul health care.

"I'm out there fighting for President Obama's health-care plan, and nobody in the Democratic caucus has been out there with four town-hall meetings," Specter said. "I put my neck on the line."

Sestak, a favorite of liberal bloggers in his two campaigns for Congress, argued that he is the true Democrat, that Specter enabled some of the worst policies of Republican President George W. Bush. Bloggers were the loudest voices urging Sestak to challenge Specter when the 28-year incumbent switched parties in April and was embraced by Obama and other top Democrats.

"President Obama was not elected . . . because of political calculation, because the establishment blessed him," Sestak said, making the sign of the cross in the air. "He did it because of audacity. He's there because he took on the issues that were large. He tackled them."

Sestak said he was "150 percent behind" a "public option" of government-run health insurance to compete with private insurers, a priority of Obama's.

He also was quick to point out that Specter had appeared to change his position on the key change. Specter said yesterday he was for a "robust public option," but Sestak pointed out that Specter said in May on Meet the Press that he opposed a public plan.

Sestak also said that his opponent had helped kill the Clinton administration's health-care overhaul plan in 1994, and that since then, 10 million more people are uninsured.

Asked how he could help Obama round up GOP votes for health-care changes, Specter said he would have sway with Republicans Charles E. Grassley of Iowa, Susan Collins of Maine, Olympia Snowe of Maine, Mike Enzi of Wyoming, and George Voinovich of Ohio.

The moderators, Philadelphia blogger Susie Madrak and Ari Melber of the Nation magazine, challenged Specter, reminding him that Grassley had repeated the false claim that the health-care reform proposals would create "death panels" that would withhold expensive care from the elderly.

"The next time I see Chuck Grassley - in fact, I'll tell you this, I will call him up today," Specter said. "I think his position . . . he is not correct." Some people in the hall started waving cell phones, yelling: "Call him now!"

Specter took the bait. "Join me backstage and watch me dial" when the forum ends, he said. Surrounded by bloggers recording and photographing him, Specter dialed Grassley on his cell phone. The Iowa senator was out, so Specter left a message.

At the beginning, Specter was asked why he was at the conference considering his long history as a Republican. He was typically candid.

"Who am I? I'm a fellow who has a good job," he said, and wants to keep it. "I'm here because I like to talk to people generally, and especially if I'm in a campaign and would like support to be reelected. I think I have some messages that will help me on that reelection."

Specter cited his record supporting abortion rights, stem-cell research, and equal pay for women to show that he was on his audience's side. He dismissed suggestions that his more frequent votes with Democrats were motivated by fear of a primary.

"I'm not trimming my sails," Specter said. "I'll defend each of my votes one by one. I don't believe in these statistical generalizations."

Specter also told the audience that he would support a cloture vote, to cut off debate and bring a measure to a vote, on a modified version of the Employee Free Choice Act, designed to make it easier for unions to organize workplaces.

When still a Republican, Specter had vowed not to support the bill because of its provision that would eliminate the need for a secret ballot to certify a union. Specter is among the senators working on a compromise to change the provision.

At a competing conference of conservative bloggers and activists at the Station Square Sheraton here last night, former Rep. Pat Toomey said "Pennsylvania citizens and increasingly American citizens are coming to the conclusion that Washington is out of control."

Toomey, who is seeking the Republican nomination for the U.S. Senate, told the Right Online gathering that there would be a massive pushback on government activism during the 2010 elections, adding that the Democrats seem bent on building a European-style social-welfare state.

"Now I'll admit France is probably a lovely place to visit, but I don't want to be France," Toomey said.

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