Wikipedia, one of the 10 most popular sites on the Web, was founded about eight years ago as a long-shot experiment to create a free encyclopedia from the contributions of volunteers, all with the power to edit, and presumably improve, the content.

Now, as the English-language version of Wikipedia has just surpassed 3 million articles, that freewheeling ethos is about to be curbed.

Officials at the Wikimedia Foundation, the nonprofit in San Francisco that governs Wikipedia, say that within weeks, the English-language Wikipedia will begin imposing a layer of editorial review on articles about living people.

The new feature, called “;flagged revisions,”; will require that an experienced volunteer editor for Wikipedia sign off on any change made by the public before it can go live. Until the change is approved—or in Wikispeak, flagged—it will sit invisibly on Wikipedia's servers, and visitors will be directed to the earlier version.

The change is part of a growing realization on the part of Wikipedia's leaders that as the site grows more influential, they must transform its embrace-the-chaos culture into something more mature and predictable.

Roughly 60 million Americans visit Wikipedia every month. It is the first reference point for many Web inquiries—not least because its pages often lead the search results on Google, Yahoo and Bing. Since Michael Jackson died on June 25, for example, the Wikipedia article about him has been viewed more than 30 million times, with 6 million of those in the first 24 hours.

“;We are no longer at the point that it is acceptable to throw things at the wall and see what sticks,”; said Michael Snow, a lawyer in Seattle who is the chairman of the Wikimedia board. “;There was a time probably when the community was more forgiving of things that were inaccurate or fudged in some fashion—whether simply misunderstood or an author had some ax to grind. There is less tolerance for that sort of problem now.”;

The new editing procedures, which have been applied to the entire German-language version of Wikipedia during the last year, are certain to be a topic of discussion this week when Wikipedia's volunteer editors gather in Buenos Aires, Argentina, for their annual Wikimania conference. Much of the agenda is focused on the implications of the encyclopedia's size and influence.

Although Wikipedia has prevented anonymous users from creating new articles for several years now, the new flagging system crosses a psychological Rubicon. It will divide Wikipedia's contributors into two classes—experienced, trusted editors, and everyone else—altering Wikipedia's implicit notion that everyone has an equal right to edit entries.

That right was never absolute, and the policy changes are an extension of earlier struggles between control and openness.

For example, certain popular or controversial pages, like the ones for the singer Britney Spears and for President Barack Obama, are frequently “;protected”; or “;semi-protected,”; limiting who, if anyone, can edit the articles.

And for seven months beginning in November, The New York Times worked with Wikipedia administrators to suppress information about the kidnapping of David Rohde, a correspondent in Afghanistan, from the article about him. The Times argued that the censorship would improve his chances of survival. Rohde escaped from his Taliban captors in June, but the episode dismayed some Wikipedia contributors.

The new system comes as some recent studies have found Wikipedia is no longer as attractive to first-time or infrequent contributors as it once was.

Ed H. Chi of the Palo Alto Research Center in California, which specializes in research for commercial endeavors, recently completed a study of the millions of changes made to Wikipedia in a month. He concluded that the site's growth (whether in new articles, new edits or new contributors) hit a plateau in 2007-8.

For some active Wikipedia editors, this was an expected development—after so many articles, naturally there are fewer topics to uncover, and those new topics are not necessarily of general interest.

But Chi also found that the changes made by more experienced editors were more likely to stay up on the site, whereas one-time editors had a much higher chance of having their edits reversed. He concluded that there was “;growing resistance from the Wikipedia community to new content.”;

To other observers, the new flagging system reflects Wikipedia's necessary acceptance of the responsibility that comes with its vast influence.

“;Wikipedia now has the ability to alter the world that it attempts to document,”; said Joseph Reagle, an adjunct professor of communications at New York University and one of a half-dozen scholars to earn a Ph.D. in Wikipedia studies (itself a discussion topic at Wikimania).

Under the current system, it is not difficult to insert false information into a Wikipedia entry, at least for a short time. In March, for example, a 22-year-old Irish student planted a false quotation attributed to the French composer Maurice Jarre shortly after Jarre's death. It was promptly included in obituaries about Jarre in several newspapers, including The Guardian and The Independent in Britain. And on Jan. 20, vandals changed the entries for two ailing senators, Edward M. Kennedy and Robert C. Byrd, to report falsely that they had died.

Flagged revisions, advocates say, could offer one more chance to catch such hoaxes and improve the overall accuracy of Wikipedia's entries.

Foundation officials intend to put the system into effect first with articles about living people because those pieces are ripe for vandalism and because malicious information within them can be devastating to those individuals.

Exactly who will have flagging privileges has not yet been determined, but the volunteer editors will number in the thousands, Wikipedia officials say. With German Wikipedia, nearly 7,500 people have the right to approve a change. The English version, which has more than three times as many articles, would presumably need even more editors to ensure that changes do not languish before approval.

“;It is a test,”; said Jimmy Wales, a founder of Wikipedia. “;We will be interested to see all the questions raised. How long will it take for something to be approved? Will it take a couple of minutes, days, weeks?”;

Wales began pushing for the policy after the Kennedy and Byrd hoaxes, but discussions about a review system date back to one of the darkest episodes in Wikipedia's history, known as the Seigenthaler incident.

In 2005, the prominent author and journalist John Seigenthaler Sr. discovered that Wikipedia's biographical article connected him to the assassinations of John F. Kennedy and Robert F. Kennedy, a particularly scurrilous thing to report because he was personally close to the Kennedy family.

Since then, Wikipedians have been fanatical about providing sources for facts, with teams of editors adding the label “;citation needed”; to any sentence without a footnote.

“;We have really become part of the infrastructure of how people get information,”; Wales said. “;There is a serious responsibility we have.”;