FOR all the human traffic that the Web attracts, most sites remain fairly solitary destinations. People shop by themselves, retrieve information alone and post messages that they hope others will eventually notice. But some sites are looking for ways to enable visitors not only to interact but even to collaborate to change the sites themselves.

Wikipedia (www.wikipedia.com) is one such site, a place where 100 or so volunteers have been working since January to compile a free encyclopedia. Using a relatively unknown and simple software tool called Wiki, they are involved in a kind of virtual barn-raising.

Their work, which so far consists of some 10,000 entries ranging from Abba to zygote, in some ways resembles the ad hoc effort that went into building the Linux operating system. What they have accomplished suggests that the Web can be a fertile environment in which people work side by side and get along with one another. And getting along, in the end, may ultimately be more remarkable than developing a full-fledged encyclopedia.

That is because Wikipedians, as they call themselves, can not only contribute whatever they want but can also edit entries posted by other writers as they see fit. Anyone who visits the site is encouraged to participate by a note at the bottom of each page that says, ''You can edit this page right now!'' While that may sound like a recipe for authorial anarchy, the quest for communal knowledge seems to have prevailed so far over any attempt to pit individual opinions against one another.

''It's kind of surprising that you could just open up a site and let people work,'' said Jimmy Wales, Wikipedia's co-founder and the chief executive of Bomis, a San Diego search engine company that donates the computer resources for the project. ''There's kind of this real social pressure to not argue about things.'' Instead, he said, ''there's a general consensus among all of the really busy volunteers about what an encyclopedia article needs to be like.''

He cited an entry on Bill Clinton as an example of how people might have different opinions on a topic but still be able to produce a consensus.

''If you don't like him or if you do like him that's fine,'' Mr. Wales said. ''But an encyclopedia article about him just really needs to stick directly to the facts. I should be able to write something about Bill Clinton that a supporter or a detractor could both agree on. And it's surprising that so far the social pressure has worked very well.''

Indeed, the Clinton entry seems to relate neutral facts about his presidency, including controversial acts like his last-minute pardons of convicted felons.

If peer pressure encourages the volunteers to strive for objectivity, it is the Wiki software system that allows the group to pool their collective knowledge. ''Wiki is kind of like a discussion group that is continuously constructing its own F.A.Q.,'' or frequently asked questions, said Ward Cunningham, a software consultant in Portland, Ore., who developed Wiki (named for the Hawaiian word wikiwiki, which means fast) in 1994. He was seeking a way to develop a programmers' discussion group that might avoid the sequential and repetitive postings that often spin a topic vigorously without yielding a consensus or even a concise record of how people have disagreed.

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.''