Web loggers who are campaigning against Senator Obama’s presidential run are accusing Google and Obama supporters of silencing them after their Web logs were marked as spam and their accounts temporarily frozen.

On Thursday, hours after publishing a post about an online petition demanding that Mr. Obama publicly produce his birth certificate, an associate professor of business administration at Brooklyn College, Mitchell Langbert, found that he could no longer access his Web log.

Google’s Blogger hosting service had suspended “Mitchell Langbert’s Blog,” which Mr. Langbert describes as “two-thirds academic stuff I’m working on and one-third politics,” until it could verify the Web log was not a “spam blog,” or a site designed solely to increase the page views of associated Web sites.

A day later Google lifted the block on the account, but the incident and earlier Web log freezes in late June have led Mr. Langbert and other anti-Obama bloggers to accuse the Illinois senator’s supporters of intentionally identifying their blog addresses to Google as spam blogs. They also say the company has reflexively suspended the sites.

“These tech-savvy smart alecks have figured out that if you report a blog you don’t like, you can do some damage to a person,” Mr. Langbert said.

A spokesman for Google, Adam Kovacevich, said in a statement that an overzealous antispam filter was responsible for the blocks.

“We believe this was 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,” he said. “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.”

Several of the blogs that were blocked, including hillaryorbust.com and comealongway.blogspot.com, are part of the “Just Say No Deal” network of anti-Obama blogs. But Mr. Langbert’s blog is not, leading him to conclude that Obama supporters had targeted him.

On her right-leaning blog “Atlas Shrugs,” Pamela Geller keeps a list of blogs that Google has temporarily blocked. “The blockings do come in waves,” she said. “The last wave was this past week, and now it got very quiet.”

Some writers have had their blogs unblocked, while others have moved them to WordPress, a rival blog host.

“I don’t think” Google has “malicious intentions at all, it’s just that spammers can literally overrun a service if you’re not careful, so their defenses have become overzealous,” a spokesman for WordPress, Matthew Mullenweg, said in an e-mail.

“We always have human review before turning off an active blog,” he said. “People invest so much time into their blogs, to treat it with anything less than the utmost respect is criminal.”