COLOMBO, SRI LANKA, OCT. 23 -- The main target of the Indian Army assault on the northern city of Jaffna, Tamil Tigers militia leader Velupillai Prabhakaran, has slipped past his Indian attackers and is believed to have set up a new base deep in the Tamil heartland of Sri Lanka, according to the senior Indian representative here.

Jyotindra Nath Dixit, the influential Indian high commissioner, or ambassador, to Sri Lanka, said today the charismatic 33-year-old Prabhakaran, who has defied the Indian Army as he did the Sri Lankan forces before them, had apparently escaped from Jaffna, possibly with most of his key lieutenants.

He said Prabhakaran's new base was thought to be near the city of Mannar about 50 miles south of Jaffna on Sri Lanka's western coast.

Prabhakaran's escape, as the Indian Army was reported to be rooting out remaining "small pockets of resistance" inside downtown Jaffna, was considered a major setback for the Indian forces seeking to end a four-year-old civil war by Sri Lanka's mostly Hindu Tamil minority.

Senior Sri Lankan officials said that for India's costly military offensive against Jaffna to be successful it would have to capture Prabhakaran and several of his die-hard lieutenants to stifle their movement to create an independent Tamil state in this predominantly Buddhist island nation.

"If the Indians can capture Prabhakaran and his chief lieutenants, then at most the separatists will only be capable of residual terrorism," said one senior Sri Lankan defense official. "But if they fail, then Prabhakaran will live to regroup and fight another day."

"The main objective of the Indian offensive in crude terms has been to capture Prabhakaran," said Neelan Truchelvam, a moderate Tamil political leader here. "If they haven't succeeded in that, they haven't done very much."

Prabhakaran, a short, plump man, has become a legend since 1975, when he burst upon the Tamil separatist stage at age 21 with the assassination of a moderate mayor of Jaffna, the capital of the Tamil-dominated northern province of Jaffna.

Prabhakaran has proven himself a ruthless, resourceful and uncompromising guerrilla leader. He has fought and defeated rivals, escaped assassination attempts and repeatedly battled superior military forces to a standstill, only to elude them at the last minute when military victory proved impossible.

Since 1975 -- with help from neighboring India -- he has welded together the Liberation Tigers of Tamil Eelam, a militia of well-armed and devoted young guerrillas who in recent years have emerged as the largest, best-armed and most fanatic of the half-dozen or so Tamil organizations advocating a separate state.

The Indian troops fighting against the Tigers in Jaffna came to Sri Lanka as a peace-keeping force in late July after India and Sri Lanka signed an agreement that sought to end the Tamil revolt and open the doors to a political solution that would give the island's Tamil minority a measure of autonomy.

The Indian force, which in recent weeks has grown with reinforcements to more than 20,000 men, was assigned to disarm the Tamil separatist groups.

Despite strong pressure from his former Indian benefactors, Prabhakaran balked at surrendering his group's arms. Last month he launched a new series of attacks on civilians of the Sinhalese majority living in northern and eastern Sri Lanka.

Prabhakaran's defiance infuriated the Indians, who had staked their prestige on being able to deliver the separatists for a political solution in Sri Lanka. On Oct. 10 India launched a full-scale offensive against Prabhakaran and an estimated 1,500 supporters entrenched in Jaffna.

The Indian Army was surprised by the tenacity of the Tamil resistance. In two weeks of fighting, 136 Indian troops have been killed and 404 wounded, and they are still fighting in the city of Jaffna, if, according to Dixit, only against deeply entrenched "pockets of resistance."

Dixit acknowledged that so far India had no information on the whereabouts of any of the major Tiger leaders.

The latest fighting has raised concerns that the Tigers could wage war against Indian forces as they have for the past four years against the Sri Lankan Army.

This afternoon a separatist mine killed an Indian officer and three soldiers outside the town of Kalamanchikude, in Sri Lanka's eastern province. According to residents of the town reached by telephone tonight, Indian troops reacted by killing 14 civilians and burning dozens of houses in the village.

"Everyone is expecting us to do in 10 days what the Sri Lankans could not do in 10 years," Dixit complained today in an interview with four western correspondents. "We know we don't have much time before everyone will turn against us here."