In a speech that mixed recollections of his presidency and political battles, former President Bill Clinton told 1,800 bloggers and progressive activists at the Netroots Nation conference last night that the Republican party is "sitting around waiting for Democrats to fail" on health care.

"They know they have no chance on health care this time unless they can mortify moderate and conservative Democrats," he told the crowd, noting that "they don't have the filibuster this time."

But the progressive community must also not get bogged down in petty disagreements over the fine points of health care policy, he added.

"It is politically imperative for Democrats to pass a health care bill now," he said, because "If you get out there and don't prevail, then the victors get to rewrite history."

"You hold the seeds of a genuine revolution in public life, and you do it by mobilizing and getting people to think," he told the enthusiastic crowd at the convention's first night keynote session. "People trust you. They believe that you believe what you put down [in blogs], they don't believe you fudge the facts. They believe you're being straight with them, and if you make a mistake it's of the head, not of the heart."

Mounting the stage about 20 minutes later than scheduled and sounding hoarse, Mr. Clinton got a big laugh when he apologized "for my voice. I've been on too many airplanes in the last few days," he said, in a not-so-subtle reference to his recent trip to North Korea to negotiate the release of two American journalists.

He noted that progressives won the White House because Republicans had "a terrible candidate, [there were] favorable conditions and the culture was with us. America is a different place today. We know we live in an interdependent country and an interdependent world.

"We have entered a new era of progressive politics, which if we do it right could last 30 to 40 years," he said.

Thanking the crowd for "elevating the level of discourse" in American politics, he noted that he'd had two sessions with bloggers in his office in Harlem recently "and I've found them very helpful." He also said that at an upcoming session of the Clinton Global Initiative, his fifth, he expects about 200 bloggers to attend, and that the initiative's work is "the next logical step in the activism you represent."

He also got a big laugh when he said, "One of the great things about being an ex-president you can say whatever you want. Of course, they don't care what you say anymore, unless your wife becomes secretary of state and then they really care if you screw up,"

About 15 minutes into his speech, he was interrupted by a heckler who challenged him for signing the Defense of Marriage Act, which gay and lesbian activists regard as discriminatory.

"You know, you ought to go to one of those Congressional heath care meetings," Mr. Clinton said, to laughter, but added that signing that bill was, in part, a way to sidetrack passage in Congress of a constitutional amendment to ban gay marriage.

"I did everything I could," he said, to promote gay rights while president.

Mr. Clinton's appearance was to cap the first day of the convention, which runs through Sunday at the David L. Lawrence Convention Center.

Today the bloggers will be able to attend a town hall meeting on health care with former Vermont governor and Democratic National Committee chairman Howard Dean.

It was Mr. Dean who coined the term Netroots, a blending of Internet activism and grass-roots supporters, during his 2004 presidential campaign.

The town hall meeting will be followed by a "Pennsylvania Leadership Forum" where Sen. Arlen Specter and his challenger in the Democratic primary, U.S. Rep. Joe Sestak, will take questions separately.

Despite the generally upbeat, celebratory mood of yesterday's conference -- the first in Netroots Nation history with a Democrat in the White House -- many speakers were already warning of a tough mid-term election year in 2010.

At one panel on polling data, experts noted that political anger and intensity has shifted to the Republican side, with Democrats facing considerable erosion of their 54-seat advantage in the House next year.

"There's offense and there's defense. Right now, you're going to be spending time on defense," said Charlie Cook of the nonpartisan Cook Political Report. "Intensity matters a lot. Last time you [Democrats] had it, this time they [Republicans] have it," Mr. Cook said, adding that he expects about a 20-seat loss in the 2010 mid-term elections.

Poll analyst Nate Silver of FiveThirtyEight.com did not agree with Mr. Cook. He expects Democrats to do even worse.

Mr. Silver said Democrats often told him his Obama-friendly polls comforted them last fall. "I don't think you should feel at all comforted about 2010," he said to a standing-room-only crowd. He said he expects Democrats will lose from 20 to 50 House seats and up to six Senate seats next year.

"The enthusiasm gap is working the other way. ... I don't know what the sales pitch is right now for Democrats."

Health care -- and the recent town hall meetings featuring angry voters yelling at legislators -- were the focus of much earnest discussion in the hallways, at panel sessions and at last night's keynote session.

"It's easy to say no to everything, but one thing I know is that the status quo [in health care] doesn't work," said Allegheny County Executive Dan Onorato, "This debate is just getting started."

Simon Rosenberg, head of NDN, a left-wing, Washington, D.C.-based think tank, said that when he first started working in Democratic politics, online communities like Netroots were unheard of.

"We didn't have the incredible ecosystem of center-left politics that has been created over the past six years. We're now at a different moment in our movement. More important work is in front of us. Now is not a time to reject the other side, but use our imagination on what kind of America to build together."

Cole Goins, a blogger from Washington, D.C., said he was pleased that Mr. Clinton's speech addressed the two main issues in the national debate: climate change and health care.

"The most important takeaways, though, weren't necessarily his opinions but the focus on the message of empowering individuals to use the technology we have today to say what we want, engage the community, and make it relevant to people," Mr. Goins said.