NEW DELHI, SEPT. 23 -- India announced today that it is sending units of its Central Reserve Police Force to bolster thousands of peace-keeping troops already deployed in neighboring Sri Lanka.

The announcement follows an outbreak of fighting between Tamil factions in the north and east of the island nation in which scores have been killed. The series of attacks and counterattacks sharply underscored the fact that militants seeking autonomy for the country's Tamil minority have kept many of their weapons weeks after a deadline for their surrender.

"There are a lot of bodies {peace-keeping troops} in there, but they aren't doing anything. So far, there has been a lot of talk on weapons, but nothing has happened," said one well-informed observer reached in the Sri Lankan capital, Colombo.

Today, Indian peace-keeping forces opened fire on a crowd besieging their camp at Mannar, in northwestern Sri Lanka. News agency reports from Colombo said one person was killed and 20 injured, but other sources interviewed by telephone said these numbers may be exaggerated.

The incident nevertheless is one of the most serious involving Indian peace-keeping units since they went to Sri Lanka under a July 29 peace agreement designed to end years of virtual civil war between the Tamils and Sri Lanka's majority Sinhalese community.

Initially, this force numbered only 3,000 or 4,000 and was restricted to the Jaffna Peninsula, the Tamil heartland in the north. Now, however, the Indian Army presence is put at 11,000 to 15,000, and the Central Reserve Police are expected to add another 4,000.

Sri Lanka's total military and police forces are believed to number no more than 36,000.

The Central Reserve Police Force is a mobile paramilitary unit used by New Delhi in situations that are too threatening for local police but not serious enough to require calling in the regular Army.

The Indian involvement in Sri Lanka's military and political affairs has raised questions in New Delhi about the initial enthusiasm for the July 29 accord. The implementation of the accord is being watched closely as a harbinger of how India plans to carry out its role as a regional power in South Asia.

Prime Minister Rajiv Gandhi appears determined to fulfill India's commitment to bring peace to Sri Lanka, although some detractors have expressed fears that he is following the same path as in India's troubled Punjab State, where a peace accord never has been implemented and the killing increases.

As the announcement of new forces was being made in New Delhi, Lt. Gen. Depinder Singh, the commander of India's forces in Sri Lanka, arrived in Jaffna, apparently to give new warnings to the Liberation Tigers of Tamil Eelam, the main Tamil guerrilla group, according to news agency reports.

India's ambassador to Sri Lanka, J.N. Dixit, also flew to Jaffna from Colombo on an undisclosed mission.

In addition to their vendetta against rival Tamil organizations, the Tigers have mounted a political counterattack in the Jaffna area in recent days, following reports of a loss of standing just after the July 29 accord was signed.

While the Tigers reportedly have reasserted themselves, at least temporarily, in the Jaffna Peninsula, the general political situation in the country's Eastern Province remains precarious. Clashes among rival Tamil militants reportedly took at least 100 lives in the Batticaloa and Amparai districts last week, after which more Indian troops were rushed to the region.

The Eastern Province is divided among Tamils, Sinhalese and Moslems in roughly equal proportions and its future is one of the major untested areas of the July 29 accord.

Meanwhile, the government of President Junius Jayawardene continues to face problems in the predominantly Sinhalese south.

A number of local officials of the ruling party reportedly have been killed in recent weeks, with the government placing the blame on left-wing Sinhalese militants. There also are reports that senior figures in the ruling party are reluctant to leave the capital for their rural homes because of the unrest.