Chinese security agents have detained an American who was "inspecting" a proposed World Bank project in northwestern China and accused him of engaging in an "illegal investigation," according to the World Bank and the man's wife.

Tibetan advocate Daja Meston, 29, of Newton, Mass., who was detained three days ago, entered China on a tourist visa and traveled to Qinghai province's remote Dulan county earlier this month to interview residents about a controversial World Bank project, according to his wife, Phuntsok Meston. The project would move tens of thousands of poor Chinese farmers to a new area with better agricultural prospects.

But critics say the project will dilute the Tibetan population in the new area, and the World Bank voted in June to delay its funding pending a bank inquiry.

Meston was detained along with an Australian scholar, Gabriel Lafitte, also a longtime advocate of Tibetan causes. A source familiar with the detentions said Chinese authorities apparently suspect that the men were "pushing a broader cause of Tibetan separatism."

On a trip to China in August 1997, Meston was the Tibetan language translator for Rep. Frank R. Wolf (R-Va.) during an unauthorized trip to Tibet. China requires foreign officials and journalists to apply for special permission to visit Tibet, and Wolf's trip in the guise of a tourist infuriated Chinese authorities.

Wolf, who described his time in Tibet as a "nightmare tour," said China was brutally repressing Tibet's people and "swallowing" its culture. China's Foreign Ministry accused Wolf of "wantonly slandering China."

A World Bank spokesman said Chinese officials called several days ago to ask if Meston and Lafitte were representing the bank on their trip, and bank officials told them no.

"We continue to believe there should be access to the site. . . . But it's a Chinese project, and it's up to the Chinese government to grant that access," said spokesman Peter Stephens.

Tibetan rights groups have framed the proposed project in Dulan as one more step in a Chinese government campaign to destroy Tibetans' distinct culture. The project has become linked in the West with the broader issue of Chinese human rights abuses in Tibet.

Chinese officials are intensely sensitive about all matters concerning Tibet and the Tibetan people in China.

World Bank officials disputed accusations that the project will help China move large numbers of ethnic Chinese into a Tibetan area. They said the plan will move 58,000 poor people, most of whom are ethnic minorities who earn about $30 per year, to a sparsely populated region.

At the time of the World Bank vote in June, Zhu Xian, China's senior representative to the bank, said China welcomes scrutiny of the project.

"My authorities will sincerely welcome and facilitate site visits by legitimate parties concerned, including executive directors, diplomats, media people, parliament members, and even NGOs [non-governmental organizations] if they are not politically hostile and not challenging China's sovereignty," Zhu said.

Project critics said the detentions prove that China's promises about open access are a sham.

"China is telling the World Bank to stay out of its business and that this is China's internal affair," said one longtime critic, who asked not to be identified. "It's hard to believe: 'We'll take your money, but we don't want anybody to ask any questions.' "

Meston's wife, a Tibetan exile, said U.S. officials told her they would try to see her husband Friday. In Washington, the State Department declined comment except to confirm the detention.

Daja Meston, the son of American hippies, grew up in a Tibetan monastery in Nepal, his wife said. Both Mestons have been very public opponents of Chinese policies in Tibet. They were arrested at a raucous protest at Massachusetts Institute of Technology during Premier Zhu Rongji's visit there in April, charged with disorderly conduct and released. Their cases are pending, Phuntsok Meston said.