When half a dozen students in Neil Waters' Japanese history class at Middlebury College asserted on exams that the Jesuits supported the Shimabara Rebellion in 17th-century Japan, he knew something was wrong. The Jesuits were in ''no position to aid a revolution,'' he said; the few of them in Japan were in hiding.

He figured out the problem soon enough. The obscure, though incorrect, information was from Wikipedia, the collaborative online encyclopedia, and the students had picked it up cramming for his exam.

Waters and other professors in the history department had begun noticing about a year ago that students were citing Wikipedia as a source in their papers. When confronted, many would say that their high school teachers had allowed the practice.

But the errors on the Japanese history test last semester were the last straw. At Waters' urging, the Middlebury history department notified its students this month that Wikipedia could not be cited in papers or exams, and that students could not ''point to Wikipedia or any similar source that may appear in the future to escape the consequences of errors.''

With the move, Middlebury, in Vermont, jumped into a growing debate within journalism, the law and academia over what respect, if any, to give Wikipedia articles, written by hundreds of volunteers and subject to mistakes and sometimes deliberate falsehoods. Wikipedia itself has restricted the editing of some subjects, mostly because of repeated vandalism or disputes over what should be said.

Although Middlebury's history department has banned Wikipedia in citations, it has not banned its use. Don Wyatt, the chairman of the department, said a total ban on Wikipedia would have been impractical, not to mention close-minded, because Wikipedia is simply too handy to expect students never to consult it.

At Middlebury, a discussion about the new policy is scheduled on campus on Monday, with speakers poised to defend and criticize using the site in research.

Jimmy Wales, the co-founder of Wikipedia and chairman emeritus of its foundation, said of the Middlebury policy, ''I don't consider it as a negative thing at all.''

He continued: ''Basically, they are recommending exactly what we suggested -- students shouldn't be citing encyclopedias.

"If they had put out a statement not to read Wikipedia at all, I would be laughing. They might as well say don't listen to rock 'n' roll either."

Indeed, the English-language version of the site had an estimated 38 million users in the United States in December, and can be hard to avoid while on the Internet. Google searches on such diverse subjects as historical figures like Confucius and concepts like torture give the Wikipedia entry the first listing.

In some colleges, it has become common for professors to assign students to create work that appears on Wikipedia. According to Wikipedia's list of school and university projects, this spring the University of East Anglia in England and Oberlin College in Ohio will have students edit articles on topics being taught in courses on the Middle East and ancient Rome.