The Wiki software, which is available free at www.wiki.org and can be installed by another site's administrator, requires no special plug-ins or downloading by the user. Each page on a Wiki-enabled site comes with a handful of links that users can click on to make changes. Mr. Wales describes the process of editing and repositioning passages as ''self-healing.'' The result is a continually updated text in which comments can be refined, mistakes corrected and duplications eliminated.

''I can start an article that will consist of one paragraph, and then a real expert will come along and add three paragraphs and clean up my one paragraph,'' said Larry Sanger of Las Vegas, who founded Wikipedia with Mr. Wales. (He also works as the editor in chief of another online encyclopedia, Nupedia, which relies on a more traditional system of peer-review editing to assemble its contents.) ''Then another expert will come along and change the whole thing to something that's even better and add in two new sections as well as a couple of new articles that sort of support the main article. It's constantly growing.''

Whether it's constantly improving is another question. While Wikipedia has entries that are comparable to what might be found in a traditional encyclopedia -- the ones on capitalism and number theory, for example -- most are clearly works in progress, marred less by mistakes than what might be called uncertainties. The Bill Clinton entry, for instance, said in late August he was ''a two (more?) time governor of the state of Arkansas.'' Within two weeks it was updated to reflect the years he served as governor. (He served six two-year terms, or 12 years over a 14-year period.)

Mr. Sanger said that the contributors consisted mainly of young men, many of them computer programmers or academics, from around the world. He said that it was important to remember that the project began only in January. ''Wikipedia is designed to be as easy as possible for anyone to change, and therefore the quality is constantly improving,'' he said.

But that unfettered ability to change entries also introduces the possibility that an opinionated renegade, not to mention a vandal, might come along and ruin the group's work. ''We've been fortunate so far,'' Mr. Wales said. ''So far we haven't had any Internet lunatics stumble upon us.''

He said that backup copies were periodically created to ensure that any destructive deletions could be reversed. But over all the project has been remarkably civil, he said, considering the name-calling that often breaks out in online discussion groups.

It is unclear, of course, whether the world needs another encyclopedia. Vast information is already available on the Web, and while much of it is scattered among disparate sites, search engines have made it easier to find it. One trend in Wikipedia's favor is the charging of fees at some sites for access to their content. In July Encyclopaedia Britannica began charging $5 a month for access.