COLOMBO, SRI LANKA, NOV. 12 -- Ethnic Tamil guerrillas set off a land mine under a bus, killing 25 people today, only hours before the Sri Lankan Parliament granted the Tamil minority limited autonomy in one-third of the country.

A military spokesman said the rebel Liberation Tigers of Tamil Eelam detonated the mine as the bus was passing Cheddikulam in the northwestern district of Mannar.

"All the passengers killed were Tamils," he said.

The Tigers are fighting for a Tamil homeland and have repudiated a peace accord signed in July by President Junius Jayewardene and Indian Prime Minister Rajiv Gandhi.

The government pushed the controversial legislation through Parliament despite protests by hard-line members of the ethnic Sinhalese community and unrest across the island in which 100 people died this week.

The opposition Freedom Party, composed of Sinhalese, denounced the legislation, saying Jayewardene had turned Sri Lanka into a pawn of India. It demanded a referendum.

The peace accord committed India to disarm the Tamil guerrillas and supervise implementation of the agreement.

At least 20,000 Indian troops are involved in the offensive against the Tamils, which the government hopes will be over by December. More than 240 Indian troops have died since Oct. 10 when the offensive was launched.

Freedom Party leader Anura Bandaranaike told Parliament before the vote that Jayewardene had betrayed the country and said the peace accord with Gandhi had resulted only in "carnage, tears, destruction and blood."

The autonomy arrangement, he said, would give the Tamils, who make up 13 percent of the island's 16 million people, 30 percent of the land and 60 percent of its coastline.

"If you think it is right to go ahead with these laws, it is a moral obligation to hold a referendum and get the consent of the people," he declared.

The backlash from hard-line Sinhalese has been violent. A car bombing Monday, on the eve of the three-day parliamentary debate, killed 32 and injured 106. Extremists fatally shot a Catholic priest and wounded a nun in the south of the country. Power lines have been cut and railway tracks uprooted.

Sinhalese students have demonstrated on at least four campuses. Police in the central highland town of Kandy used tear gas and batons to disperse antigovernment student demonstrators yesterday.

Police have blamed much of the violence on an outlawed Marxist group, called the People's Liberation Front, opposed to the autonomy plan.

The legislation, which passed 136 to 11 with two abstentions, clears the way to set up provincial councils in a unified northern and eastern Tamil area and in each of the seven Sinhalese-dominated districts to the south. A second bill amends the constitution to provide for the councils.

The legislation cost Jayewardene the resignation of his agriculture minister, Gamani Jayasuriya, who said he was opposed to the unification of the northern and eastern districts.

Political sources said a ruling party member who voted against the laws and two others who abstained were expected to face disciplinary measures against them.

Prime Minister Ranasinghe Premadasa, who earlier had indicated he was against some of the provisions, told Parliament that he was voting in favor because it did not violate the unitary status of the constitution.