Under strong pressure from India, Tamil separatists left here today for talks with Sri Lankan government officials aimed at settling an ethnic dispute that has brought that island nation to the brink of civil war.

Representatives of five Tamil separatist organizations originally threatened to boycott the talks, which start Monday in Thimpu, the capital of the isolated Himalayan kingdom of Bhutan. But the militants reluctantly changed their minds after meetings here yesterday and today with Indian officials who arranged the peace talks and a cease-fire that has held for nearly three weeks.

Joining the radical separatists on the flight to Thimpu are more moderate Tamil political leaders who formed the official Sri Lankan opposition party until they walked out of Parliament over the issue of an oath of loyalty to the government. India provided the airliner for the trip to Thimpu.

K. Umamaheswaran, secretary general of the People's Liberation Organization of Tamileelam, one of the separatist groups, said he met with Indian Foreign Secretary Romesh Bhandari, who offered no incentives to get his group to the talks. "He asked us to participate," said Umamaheswaran.

This is the first time militant Tamil separatists have joined in talks with the Sri Lankan government.

It is part of a three-pronged, high-risk effort by India to end the pattern of Tamil attacks and government reprisals that has turned lush, tropical Sri Lanka into a battleground.

India is pushing Sri Lankan President Junius R. Jayewardene to be more forthcoming toward the Tamil minority's demands for regional autonomy, urging opposition politicians of the Sinhalese majority to support the government's conciliatory moves, and clamping down on Tamil separatists who have taken sanctuary among their ethnic brothers in the southern Indian state of Tamil Nadu.

At the same time, New Delhi reassured the Jayewardene government that it opposes the separatists' aim of establishing an independent Tamil state -- which would be called Eelam -- in Sri Lanka's Northern and Eastern provinces. Prime Minister Rajiv Gandhi, in a meeting here a month ago with the Sri Lankan president, also said that India would not go along with Tamil demands to meld the Northern and Eastern provinces into one, which would give the Tamils greater control there.

India's approach reflects the changed policies of Gandhi toward its smaller and less powerful south Asian neighbors. It stands in stark contrast to the position of his late mother, Indira Gandhi.

Sri Lankan Minister of National Security Lalith Athulathmudali, in an interview in Colombo two weeks ago, called Gandhi's opposition to a Tamil state "the most positive statement any Indian prime minister has made."

"It is a clear recognition that Eelam is not in India's national interest. So the Eelam movement must negotiate," he continued.

The new message from India was not lost on people in Jaffna, the almost completely Tamil city on the northern Sri Lankan peninsula, where the separatist movement has drawn its greatest support.

"Without the support of India, the militants cannot do anything," said the Rt. Rev. B. Deogupinnai, the Roman Catholic bishop of Jaffna, who is considered by the Sri Lankan government to be a strong supporter of the militant fighters.

But the highly visible Indian role in trying to solve Sri Lanka's ethnic differences carries great risk for Gandhi, who faces a possible revolt in four south Indian states that have close ties with Sri Lankan Tamils and are ruled by regional parties not under his control. India faces its own separatist movement by the Sikhs in Punjab, the nation's breadbasket on the strategic border with Pakistan.

According to informed diplomats and high government officials interviewed during a visit to Colombo, the United States has been pressing Sri Lanka to seek India's aid in resolving Sri Lanka's ethnic differences and to give up attempts to defeat the separatists militarily.

Jayewardene's meeting here in early June with Gandhi was the turning point, according to diplomats and officials.

Jayewardene, 78, always suspicious of Indira Gandhi, developed a trust in the straight-talking new prime minister, 40, who gave the Sri Lankan president specific assurances that led to the declaration of a cease-fire two weeks later.

An alleged massacre by Tamil fighters May 14 that left nearly 150 Sinhalese civilians dead in the north central town of Anuradhapura, site of one of the holiest Buddhist shrines in Sri Lanka, appears to have prompted the government to accept the Indian offer for talks.

It was the first time that Tamils were reported to have moved out of territory considered friendly to them to attack Sinhalese civilians.

The massacre was apparently part of a cycle of bloody retaliatory acts by both government forces and Tamil militants. An alleged massacre May 9, in which Army forces were reported to have killed 70 Tamils in the fishing village of Velvettiturai, was believed to have sparked the raid on Anuradhapura. The Anuradhapura attack was followed by an attack on Tamil civilians on a ferry from the island of Delft to Jaffna, which Tamils blamed on the Sri Lankan Navy.

Both the Army and the Navy denied involvement in the Velvettiturai and ferry attacks, but Jayewardene in the past has acknowledged excesses by government security forces. Now, for the most part, the killing has stopped as the cease-fire largely has been honored.

The opposition Sri Lanka Freedom Party, headed by Anura Bandaranaike, originally opposed the possibility of a settlement and accused the government of selling out Sinhalese interests. But Bandaranaike's mother, former prime minister Sirimavo Bandaranaike, gave her grudging approval to the Thimpu talks, reportedly under intense pressure from India, in a statement issued in Colombo today.