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, Jimmy Wales, founder of the St. Petersburg, Fla.-based Web site, said Monday. 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 hopes the registration requirement will limit the number of articles being created.

While it would not 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, defaming 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 Monday. “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 by just about anyone, often without having to volunteer 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.