The crash of an Air-India jet appeared today to have isolated the extreme wing of the Sikh separatist movement as most Sikh leaders here and abroad joined in condemning what is generally accepted here as a terrorist bombing.

The possible sabotage of the plane, which plunged into the sea Sunday off the coast of Ireland killing all 329 passengers and crew members, was denounced by a broad spectrum of Sikh leaders -- including some who had been labeled extremists themselves.

Among those condemning the crash of the Air-India plane were Sikh leaders Jagjit Singh Chauhan, who applauded the assassination of prime minister Indira Gandhi last October by Sikh bodyguards, and Joginder Singh, father of an extremist leader killed last June when the Indian army stormed the Golden Temple, the holiest Sikh shrine.

The All-India Sikh Students Federation, one of the most radical Sikh groups here and the backbone of the separatist movement, denied any role in the downing of the plane. An anonymous caller to The New York Times, purporting to represent the Sikh Student Federation, earlier had claimed responsibility for setting a bomb on the Air-India jet.

"That's one positive element. The lunatics have been really put aside for the first time," said Sikh historian Khushwant Singh, a member of India's upper house of Parliament.

Although investigators are theorizing that terrorist bombs caused the crash, no proof has yet been presented.

Sikhs, followers of a 500-year-old religion combining elements of Hinduism and Islam, have been pressing the government for more autonomy for the state of Punjab, the country's breadbasket where many of them live.

Militant Sikhs are seeking to avenge the Golden Temple attack and a wave of anti-Sikh rioting by Hindus last November following the assassination of Indira Gandhi, mother of the present Prime Minister Rajiv Gandhi.

Meanwhile, Prime Minister Gandhi is trying to meet some of the Sikh demands in the Punjab. He told The Indian Express today that he sees a chance for a solution there and added that the condemnation of the Air-India crash by such Sikh political leaders as Harchand Singh Longowal, president of the Sikh political party, has created a better atmosphere for a reconciliation between Sikhs and Hindus, who make up the vast majority of this nation of 735 million.

"What the Sikh extremist organizations are truly interested in again is communal riots against Sikhs. They want another round of frenzy to destroy any chance of reconciliation between the government and the Akalis the Sikh political party, " wrote M.J. Akbar today in the Telegraph, a Calcutta newspaper.

Following Indira Gandhi's assassination by two Sikh bodyguards, a subsequent backlash by Hindus left thousands of Sikhs dead, injured or homeless as slum-dwelling mobs slaughtered members of the religious minority on trains, buses and city streets.

That bloodletting left many Sikhs questioning whether they will ever be accepted again as full partners in the Indian nation, while at the same time creating doubts among Hindus as to whether Sikhs could be trusted. While they make up only about 9 percent of India's population, Sikhs hold a disproportionate share of high ranks in the police and military services. They also have the reputation of being industrious businessmen and form the backbone of transportation in northern India.

All Sikhs have Singh, which means lion, as part of their name and are distinguished by their unshorn hair worn under a turban and their full beards. Unlike the Gandhi assassination, no anti-Sikh violence has followed the Air-India crash or the terrorist bombings by Sikh extremists here and in other parts of India in May that killed at least 80 people.

But there is considerable anti-Sikh feeling in India, according to historian Singh. Some of this feeling has spread to Sikh communities in other countries, especially Great Britain, where B.K. Tiwari reported in The Indian Express today that the "extremists are an embarrassment to innocent and moderate Sikhs who want to be left in peace and are debating among themselves what to do with those who are harming the Sikhs' interests."

In Washington, the chairman of the Sikh Association of America accused the U.S. media of being "prompted" by the Indian government "which is desperately trying to portray the entire Sikh community as a group of terrorists."

Most of the victims of the crash appeared to be Indian emigrants who were returning to their homeland -- many with their families -- for summer holidays, airline officials said.

According to R.K. Thadani, Air-India's regional director, no definitive list of nationalities is yet available here. But he said only about 15 of the names on the passenger list were not of Indian origin. The rest of the passengers had "distinctly Indian" names, he said.

Another airline official said the passengers included about eight American citizens of Indian origin. More than 80 children were on board, including at least four infants, airline officisls said.

They said there was no accurate list of Sikhs on the passenger list. As many as 60 of the victims may have been Sikhs. Canada, where the flight originated, has sizable Sikh communities.

Among the victims, according to press reports here, were Balbir Singh, an economics professor at Montreal University, and his wife and three daughters.

Like many other passengers, they were returning to India to see relatives during summer holidays.

Others included Anumita Gupta, a Canadian-born 16-year-old student who was on her way to Calcutta to see her grandparents.

At least half a dozen passengers were young women returning to India to be married.