SAN FRANCISCO — Wikipedia, the online encyclopedia to which anyone can contribute, is tightening submission rules after a prominent journalist complained that an article falsely implicated him in the Kennedy assassinations.

Wikipedia will now require users to register before they can create articles, said Jimmy Wales, founder of the St. Petersburg, Fla.-based Web site, yesterday. People who modify existing articles will still be able to do so without registering.

The change comes less than a week after John Seigenthaler, a one-time administrative assistant to Robert Kennedy, complained in an op-ed published in USA TODAY that a biography of him on Wikipedia claimed he had been suspected in the assassinations of the former attorney general and his brother, President John F. Kennedy.

Wikipedia, often cited as a prime example of the type of collective knowledge-pooling that the Internet enables, has some 850,000 articles in English as well as entries in at least eight other languages, including Italian, French, German and Portuguese.

Since its launch in 2001, it has grown into a storehouse of information on topics ranging from medieval art to nanotechnology.

The volume is possible because the site relies on volunteers, including many experts in their fields, who submit entries and edit previously submitted articles.

Wales said he hoped the registration requirement would limit the number of articles being created.

Though it won't prevent people from posting false information, the new process will make it easier, said Wales, for the site's 600 active volunteers to review and remove factual errors, defamatory statements and other material that runs afoul of Wikipedia policy.

Wikipedia visitors will still be able to edit content already posted without registering. It takes 15 to 20 seconds to create an account on the Web site, and an e-mail address is not required.

"What we're hopeful to see is that by slowing that down to 1,500 a day from several thousand, the people who are monitoring this will have more ability to improve the quality," Wales said. "In many cases the types of things we see going on are impulse vandalism."

The episode demonstrates the lack of accountability that often comes with articles posted by anonymous people over the Internet. Unlike content included in magazines, books and other traditional media, online material can be submitted to a site such as Wikipedia by just about anyone, often without any identifying information.

"I sympathize with this person, but it's really not any different than a posting on an anonymous Web page," Eugene Volokh, a law professor specializing in the First Amendment, said, referring to Seigenthaler. Volokh added that Wikipedia provides casual readers with a valuable service but that he would never rely on it as a source for scholarly articles.

Seigenthaler, USA TODAY's founding editorial director, a former president of the American Society of Newspaper Editors and the founder of the First Amendment Center, said that after the op-ed was published Wikipedia's biography of him was changed to remove the false accusations.

But Seigenthaler said an entry yesterday still got some facts wrong, apparently because volunteers were confusing him with his son, a journalist with NBC News.

Also disturbing is a section of his biography that tracks changes made to the article, Seigenthaler said. Entries in that history section label him a "Nazi" and say other "really vicious, venomous, salacious homophobic things about me," he said.

Wales said those comments would be removed.

For 132 days, Seigenthaler said, the biography of him falsely claimed that "for a brief time, he was thought to have been directly involved in the Kennedy assassinations of both John, and his brother, Bobby."

The biography also falsely stated that he had lived in the Soviet Union from 1971 to 1984.

Seigenthaler said he wasn't convinced the new registration requirement would stop the practice of vandals' posting content that is slanderous or knowingly incorrect.

Wikipedia will either have to fix the problem or will lose whatever credibility it still has, he said.

"The marketplace of ideas ultimately will take care of the problem," Seigenthaler said. "In the meantime, what happens to people like me?"