COLOMBO, SRI LANKA, JUNE 15 -- Fierce battles between government troops and separatist Tamil rebels intensified across the north and east of this lush tropical island today, raising fears that another brutal civil war is erupting in a country that has been ravaged by internal conflict for much of the last decade.

Government forces deployed armed helicopters, other military aircraft and naval gunships against rebel positions in an attempt to support several thousand infantry reinforcements moving toward besieged army positions in the north and east, a Sri Lankan military official said. The reinforcements are making slow progress because of land mines and fears that separatist guerrillas have planned ambushes on the overland routes to the northeast, the official said.

Tamil rebels launched fresh assaults today against army bases near the port city of Trincomalee and south along the island's eastern coast, government and military officials said. The rebels also continued to take control of police stations throughout the northeast, capturing weapons and money from the poorly defended government compounds.

{Military sources said columns of soldiers advanced on the towns of Trincomalee, Mutur, Pottuvil and Vavuniya and retook the police stations there, the Reuter news agency reported.}

Sri Lankan military officials and some witnesses who have made their way from the northeast estimate that between 200 and 300 people may have died since fighting erupted earlier this week.

Casualty figures were sketchy because civilian communication lines have been severed and government security forces in the affected areas are reportedly pinned down at army bases, unable to move through towns or into the surrounding jungles, which are largely controlled by the Tamil Tigers.

Sri Lankan officials said at least 600 policemen have been reported missing and are believed to have been captured by the Tamil rebels. There have been unconfirmed reports by the Sri Lankan military that the rebels have executed a large number of the policemen, but a rebel spokesman has said no policemen have been killed.

Cease-fire negotiations were renewed between the government of President Ranasinghe Premadasa and the dominant guerrilla force in the north, the Liberation Tigers of Tamil Eelam. A statement issued by the Ministry of Defense tonight said that after talks today in the northern city of Jaffna, both sides "agreed that every step should be taken as early as possible to restore normalcy."

But there were few indications that a truce would be struck or abided by soon. The guerrillas violated cease-fires declared earlier this week.

The renewed violence comes just as Sri Lanka, a popular tourist destination with a once-booming, Western-oriented economy, was making tentative steps toward peaceful recovery from several years of devastating civil conflict.

The roots of the island's recent conflicts lie in its bitter ethnic division between a majority Sinhalese population, located mainly in the south, and the minority Tamils, who dominate the north. Each group has accused the other of unfairly exploiting its position on the island to win jobs and privileges. For years, Tamil militants have demanded an independent homeland in the north and east, an aspiration rejected by the government.

Ethnic riots and warfare between Sinhalese and Tamils during the mid-1980s prompted India to send 50,000 troops to the island under a bilateral accord signed in 1987. Tamils constitute a large ethnic group in India, and the Indian troops at first came to protect the Sri Lankan Tamils from the southern Sinhalese. But later the Indians wound up fighting a costly counterinsurgency war against the Tamil Tigers, the strongest and most militant of the Tamil separatist groups then in the north.

The presence of Indian troops on the island helped provoke a violent uprising by Sinhalese revolutionaries in the south. During 1988 and 1989, as Indian troops battled the Tigers in the north and Sri Lankan forces launched a brutal crackdown against the Sinhalese radicals in the south, the island descended into chaos and carnage. An estimated 20,000 people died during the period and the country's tourist and export economy nearly collapsed.

A fragile peace emerged earlier this year when the demoralized and beaten Indian troops went home, leaving the entire north and east in the hands of the Tigers. At the same time, the government's crackdown in the south, which included support for vigilante death squads that carried out widespread executions of civilians, defeated the Sinhalese radicals.

President Premadasa, the architect of Sri Lanka's bloody peace, hoped to build on these accomplishments this summer by negotiating a political autonomy agreement with the Tigers, essentially ceding control of the north and east to the Tamil guerrillas in exchange for preservation of the national union and a lasting cease-fire.

But talks between Premadasa and the Tigers began to stagnate in recent weeks because the Tamil guerrillas adamantly refused to lay down their weapons and the government moved slowly on promises for political reforms. It is not clear whether the Tigers' attacks on government security forces which ignited this week's open warfare marked a premeditated plan by the guerrillas to abandon dialogue with Premadasa or simply escalated from minor skirmishes.

However, in recent weeks, the Tigers have been busily constructing concrete bunkers, military posts and docks for moving weapons and wounded by sea, according to Sri Lankan government officials and independent witnesses who have traveled in the northeast.