THE TRAGEDY unfolding in the South Asian state of Sri Lanka, known as a showplace of democracy and development, finds its causes in historic tensions between the Buddhist Sinhalese majority and the Hindu Tamil minority. Tamil terrorists upset the balance two years ago, and the government's hesitations and the army's excesses have since made a bad situation worse. It appears that the struggle may be moving past the point of political return.

Americans and others are advising the government, even as it fights the terrorists, to ensure that the army treats the non-guerrilla Tamil population more carefully and to renew its search for a political settlement. This is good advice, but there is a sinking feeling all around that it is not enough.

It is not enough, for one reason: Sri Lanka faces an extremely difficult situation in India. Sri Lanka's Tamils have close connections to the 45 million ethnic Tamils in India's Tamil Nadu state -- which lies, at its closest point, just an hour's speedboat ride away across the Palk Strait. The late Indira Gandhi allowed the Sri Lankan separatist army to train and stage in Tamil Nadu. Her successor as prime minister, her son Rajiv, is regarded as more receptive to Sri Lankan complaints, but nationalist sentiment still makes it difficult to crack down on the "Tamil tigers." Guerrillas acknowledge to reporters that the supply line across the water remains open.

Unfortunately, there is more. It is pointed out that Sri Lanka's Tamils, making up barely 12 percent of the population, can hardly expect on their own to force a partition and to set up and sustain an independent state. There is a suspicion that the terrorists' real strategy may be to provoke Sinhalese repression against Tamil civilians on a scale that would precipitate an Indian "peace-keeping" intervention. In the region, few have forgotten how Indian forces carved Bangladesh from Pakistan in 1971.

Rajiv Gandhi has assured visitors that India has no intention of a military intervention in Sri Lanka. But the situation on the ground is deteriorating. Terrorism, as India's own recent Sikh explosion amply demonstrated, hardens all sides. The first responsibility for what happens in Sri Lanka falls on the government in Colombo. But India also has a heavy responsibility, and it is not fulfilling it.