(UPDATE 7:20 p.m.| Added comment from one of the bloggers who was shut down by Google.)

Did Google use its network of online services to silence critics of Barack Obama? That was the question buzzing on a corner of the blogosphere over the last few days, after several anti-Obama bloggers were unable to update their sites, which are hosted on Google’s Blogger service.

The bloggers in question, most of them supporters of Senator Hillary Rodham Clinton, and all of them opposed to Senator Obama, received a notice from Google last week saying that their sites had been identified as potential “spam” blogs. “You will not be able to publish posts to your blog until we review your site and confirm that it is not a spam blog,” the Google e-mail read.

Many of the bloggers were affiliated with JustSayNoDeal.com a Web site that opposes Senator Obama. They include http://bluelyon.blogspot.com, http://comealongway.blogspot.com, http://hillaryorbust.blogspot.com and http://mccaindemocrats.blogspot.com.

In an article that appeared on Bloggasm.com, the reporter Simon Owens spoke with some of the affected bloggers, who said they believed that Google had fallen prey to a campaign by activists supporting Senator Obama. According to the bloggers, the Obama supporters had clicked on a “flag” on the anti-Obama blogs alerting Google that they were spam.

If so, that would be an embarrassment for Google. On its Web page explaining the “flag” feature, Google says that “it can’t be manipulated by angry mobs. Political dissent? Incendiary opinions? Just plain crazy? Bring it on.”

On Monday, Google would not explicitly rebut the idea that it had been tricked but said that the cause of the temporary blockage appeared to be elsewhere. “It appears that our anti-spam filters caused some Blogger accounts to be blocked from creating new posts,” Google spokesman Adam Kovacevich said in a statement. “While we are still investigating, we believe this may have been caused by mass spam e-mails mentioning the ‘Just Say No Deal’ network of blogs, which in turn caused our system to classify the blog addresses mentioned in the e-mails as spam. We have restored posting rights to the affected blogs, and it is very important to us that Blogger remain a tool for political debate and free expression.”

Mr. Kovacevich would not give further details about Google’s spam monitoring techniques or their relationship to the Blogger service.

Some blocked bloggers have reported that their sites have suddenly become unblocked. Yet some have already moved their blogs to WordPress, a rival blogging service, and remain angry about what they call Google’s “guilty until proven innocent” policy.

“Without any notice, apology, or explanation, my posting privileges has been reinstated,” wrote the author of the blog Come a Long Way, who identifies herself as GeekLove. “Blogger’s ‘guilty until proven innocent’ approach is appalling. As bloggers, it is a good thing we still have choices, and I have exercised my choice to leave Blogger and establish a new home at WordPress.”

Attempts to reach some of the anti-Obama bloggers were not immediately successful.

Carissa Snedeker, of Silver Springs, Nevada, whose Blue Lyon blog was affected by the temporary freeze, said she doesn’t buy Google’s answer and still believes that Obama supporters “flagged” her blog. Yet she is mostly upset at Google.

“What frustrated me was that Blogger didn’t give us the benefit of the doubt,” said Ms. Snedeker, adding that she has been publishing her blog for three years. “It would have taken a human five seconds to figure out we are not spam,” she said. Her blog is now hosted on WordPress.