An American freelance journalist and longtime critic of Indonesia's rule in East Timor has said he fears Indonesian authorities will put him on trial and imprison him for entering the country in defiance of a government ban, his friends and associates said today.

Allan Nairn was detained by Indonesian soldiers at an army checkpoint in East Timor in the pre-dawn hours of Tuesday and flown to western Timor, where he is being held at an immigration detention house. Despite the government ban, he entered East Timor to report on the Aug. 30 independence referendum, and he remained behind after most others evacuated to report the post-vote rampage through Dili, the territorial capital, by anti-independence militias and Indonesian army troops.

Nairn had entered Indonesia on a two-month tourist visa issued upon his arrival--a common practice that is prohibited for working journalists but is seldom prosecuted. He also stayed longer than the visa allowed. Each act is punishable by a fine and a maximum of five years in prison, but violators are usually deported.

Diplomatic sources said that cases of journalists entering Indonesia illegally rarely, if ever, go to court, and that it was first assumed that Nairn also would be deported. But Nairn has been a frequent and outspoken critic of Indonesia's military and its brutal practices in East Timor. He was at Dili's Santa Cruz cemetery in 1991 when soldiers gunned down scores of civilians, and he has frequently slipped into East Timor despite being on a government blacklist.

In a telephone call to journalist Amy Goodman in New York, Nairn said the local prosecutor in Kupang, in western Timor, decided he should face trial. But senior national government officials in Jakarta, including the justice minister, Muladi, could overrule the local authorities.

Nairn had been reporting for Goodman's "Democracy Now" on Pacifica Radio and wrote an editorial, "U.S. Complicity in Timor," in the Sept. 27 issue of the Nation.

Senators Paul D. Wellstone (D-Minn.) and Russell Feingold (D-Wis.), the Committee to Protect Journalists and several writers have urged the State Department to demand Nairn's release. Department spokesman James B. Foley said Tuesday that Nairn "ought to have been allowed to cover the situation there."