They'll be streaming into the David L. Lawrence Convention Center, ready to join a popular American politician and do battle on the signature issues of the day: the economy, Iraq and Iran, global warming.

No, not the G-20. That's next month, when leaders of 19 nations (plus the European Union) arrive in Pittsburgh.

This week, it's a single nation's turn -- Netroots Nation, as this particular conference bills itself. And the just-announced high-profile keynote speaker for the Thursday opening is former President Bill Clinton.

The citizens of this nation, about 2,000 strong, define themselves as the netroots, lower case version -- liberal bloggers who use the Internet and grassroots activism to promote their causes and candidates. Mr. Clinton met with bloggers in June, and yesterday Netroots made the announcement that he would open the convention.

"At a time when we're all working together to make sure we get the change we voted for, President Clinton's message is spot-on. After all, holding our leaders accountable is one of the things bloggers and activists do best," said Netroots Nation Executive Director Raven Brooks.

In addition to Mr. Clinton, the convention will feature a session with President Barack Obama's senior adviser, Valerie Jarrett. There will be dozens of panels, on subjects cerebral and practical: "Online Congressional engagement beyond Twitter," and "A New Progressive Vision for Church and State."

Washington insiders Mark Blumenthal and Charles Franklin of Pollster.com and Charlie Cook of Cook's Report will show attendees how to get the most out of polling data. Another panel will discuss food politics in the Obama era. There will be "keynote" sessions, screenings and caucuses, too -- attendees can choose "identity," "issue" or "regional." And if you're a shy type, there's even a "Lurker's Caucus."

The media will be in attendance, at least the left-wing variety: Ron Reagan Jr. is broadcasting his Air America Radio show live. Conservatives will weigh in, too, across the river at the Sheraton Station Square Hotel, where the conservative group Americans for Prosperity is mounting a smaller counterconvention.

There will be parties, too. MoveOn.org is hosting a fete for graphic artist Shepard Fairey, who created the Obama "Hope" poster, Friday at the Andy Warhol Museum. DailyKos plans to hold a party for bloggers at Altar Bar in the Strip -- with Pittsburghers, certainly, but mostly with other bloggers and the politicians, pollsters, and special interest groups they blog about.

Now in its fourth year (for the first two, it was dubbed YearlyKos, after the pre-eminent liberal activist blog Daily Kos), Netroots Nation chose Pittsburgh because "we wanted to be able to green the convention easily," said spokeswoman Mary Rickles, noting that the David L. Lawrence Convention Center is the first and largest LEED-certified center in the country.

She also cited the city's strong union ties, technical innovations and grassroots activism as other factors.

Western Pennsylvania may not be known as a hotbed of liberal activism, but having the convention here not only allows organizers "to bring together existing local progressive communities, but also create new ones," she added, "to bring in progressive activists and surrounding states like Ohio, Indiana and Kentucky."

In previous years, this newly minted chattering class of laptop-wielding activists generated plenty of attention from politicians and members of the mainstream media.

In Las Vegas in 2006, presidential aspirant Mark Warner spent $50,000 on a party featuring Elvis impersonators and ice sculptures. There was an open bar at Gen. Wesley Clark's soiree at the Hard Rock Casino and New Mexico Gov. Bill Richardson bought everyone breakfast.

At 2007's Chicago conference, all but one of the Democratic candidates showed up and Fox's Bill O'Reilly sent a camera crew to confront one of the sponsors, JetBlue's CEO. Hillary Clinton made news when she defended lobbyists as "ordinary" Americans, like everyone else. Last year's conference in Austin, Texas, featured Nancy Pelosi and "surprise guest" Al Gore.

This year, though, the liberal netroots don't have George W. Bush to kick around anymore.

"This year isn't about elections, this is about legislation, and it's a much more complicated world now," said Adam Bonin, a Philadelphia lawyer who writes about legal issues for Daily Kos and who chairs Netroots Nation's board. "It's not a binary game, with Democrats good, Republicans bad."

So given this complexity, does Netroots Nation still matter?

"I think absolutely we're just as relevant," says Markos Moulitsas Zuniga, aka Daily Kos, and author, with MyDD political blogger Jerome Armstrong, of "Crashing The Gate: Netroots, Grassroots and The Rise of People-Powered Politics." Despite a lull after the November election, DailyKos.com, which features numerous bloggers with followings of their own, is setting online traffic records.

"As swamped as we were back in October 2008, we're crushing our numbers from that time, confounding the know-nothings who predicted our site traffic would plummet," he said.

In addition to Mr. Clinton and Ms. Jarrett, Sen. Arlen Specter will appear at a session with his Democratic challenger, U.S. Rep. Joe Sestak. New Jersey Gov. Jon Corzine will also be at a panel on the economy, and former Democratic National Committee Chair Howard Dean will host a town hall meeting on health care.

For myriad special interest groups attending, Netroots Nation presents an invaluable chance to network, said Jen Nessel, who coordinates communications for the Center for Constitutional Rights in New York.

"I mean, it's a blogger's convention, right? For us, as an advocacy, education and litigation group, these are people we need to get our messages out to so they can echo them."

Ron Reagan Jr. sees this meeting as a rich feast for political activists concerned about health care reform, gay civil rights and global warming, noting it's up to liberal bloggers, not the mainstream media, to control the message.

For all the hype about being a new political movement, the netroots have met with mixed success in electing their favorites. They played a key role in the candidacies of U.S. Sen. Jim Webb, D-Va., and U.S. Rep. Patrick Murphy, D-Bucks County.

But Howard Dean not only didn't become president in 2004, he was shut out of a job in the Obama administration by his enemies there. Ned Lamont failed to unseat U.S. Sen. Joe Lieberman in Connecticut. Democratic presidential candidate John Edwards tanked even before news of his infidelity became known.

But Congressional leaders "have really reached out to liberal bloggers -- they ask their advice, they hold special blogger conference calls, even hire some of them."

The netroots movement may be maturing, but it hasn't lost its mojo, he said. The right wing may be thriving on talk radio and cable news in this age of Obama, he said, but "we still outorganize and outhustle them on the things that matter.

"We build the villains and the heroes, and these days there are plenty of villains," he said.