Washington -- Barack Obama's Web site is by most accounts the best in his business. It is critical to the campaign's record-breaking fund-raising, nimble grass-roots organizing and image as a broad-based, participatory force for change.

But the very virtues of this wiki-world carry peril.

For the first time in the history of presidential politics, outside observers -- including journalists and political enemies -- have real-time access, complete with search engine, to the thinking, debating and strategizing of the vast cadre that embodies a campaign without being under the campaign's effective control.

MyBO, as the my.barackobama.com site is called, has more than 700,000 registered members. There are more than 10,000 different affinity groups based on geography, identity, ideology, occupations, hobbies and habits (Smokers for Obama, for one).

Thousands blog, at least intermittently. Members accumulate points for every activity. Too vast to vet, the site must rely on self-discipline and self-policing.

And it is becoming apparent that some forces can and will use provocative statements on MyBO against the candidate.

"When you have so many voices speaking, saying so many different things, it gives you a lot of ammunition to launch attacks on Obama," said political scientist Kevin Wallsten, who, at the University of California at Berkeley, just finished his dissertation on the blogosphere's effect on the last presidential campaign.

His point isn't lost on MyBO's members.

"Opposition groups are scouring this Web site for material to use against Obama and finding lots of hateful, extreme material," warned Birdalone, the online name used by the moderator of MyBO's International Relations Forum, in a post April 9. (Some MyBO groups are moderated, others are not.)

Wallsten said MyBO's social networking was unique among the remaining major presidential campaigns.

Obama is the only guy who is allowing this to go on on his site . . . It's benefited the view that his is a campaign-slash-movement-for-change," he said.

But it means Obama is also alone in having to contend with the mischief opponents can make of it.

"These are things that Hillary Clinton with a more traditional kind of Web site doesn't have to deal with," Wallsten said, noting that John McCain's Web site is far more rudimentary than Clinton's.

How should or can the campaign react without messing with MyBO's -- and perhaps its own -- essential mojo?

After all, "This campaign is not just a campaign, it's a movement," said Kevin LaFleur, a former Marine who grew up in Vermont and, at 28, is studying ethics, peace and global affairs at American University in Washington.

Obama's people are officially mum, ignoring a reporter's requests for an interview with any of the 20-something honchos in command.

However, there is evidence things are tightening up.

LaFleur, who already belongs to 64 different Obama groups, recently tried to launch a new one -- White Folks for Obama. His intent was not to provoke but to disarm, his point being that throughout the process white folks have supported Obama in large numbers and will continue to do so. The powers that be stalled him. Instead, he and his girlfriend created a Web site for the group off MyBO.

Meanwhile, in Wilkes-Barre, Pa., Bill Levinson, a Republican management consultant, trolls MyBO for comments about Israel and the United States that might stoke the concerns of some Jews about the Obama campaign. He posts them on his blog on Israpundit, a right-wing, pro-Israeli Web site.

On April 13, under the headline "Obama Blogger: U.S. and Terrorists are Morally Equivalent," Levinson sampled from a long MyBO posting two days earlier in which Mark Levin suggested that Americans have a blinkered view of the world, that in recent decades the Judeo-Christian West has more blood on its hands than Islam, and that the Israeli-Palestine conflict ought to be seen as "a clash of two equally valid worldviews, a clash of two rights, instead of as a clash between right vs. wrong."

But to call him an "Obama blogger" was unfair, Levin wrote to Levinson: The campaign "has no control over content posted on these blogs, I think, unless they are abusive in nature." He added, "in any big-tent campaign, you will get party-line people and then nutjobs' like me, whom Obama would run away from."

Levinson argues that if the Obama campaign leaves objectionable posts up, it is effectively sanctioning them, and that they are of a piece with Obama's association with other "unsavory" figures like the Rev. Jeremiah Wright.