Tariq Ali, a Pakistani radical who has been active in British left-wing student circles, turned up recently in Calcutta, where he was reported encouraging secessionist tendencies in both West Bengal and East Pakistan with the aim of promoting a united socialist Bengal.

"The revolutionary movement has a big opportunity in Bengal," Mr. Ali told a British reporter. "This is a heaven- sent opportunity which we should not miss. What I see in the future is the distinct possibility of India and Pakistan disintegrating-and Bengal is the spark."

Mr. Ali's radical vision of chaos on the Indian subcontinent cannot be taken lightly. The Pakistan military government's brutal crackdown on a popular democratic movement that sought a large measure of autonomy for East Pakistan has set the stage for an increasingly violent and radical reaction in the long-neglected and much-abused eastern state.

A prolonged guerrilla conflict in East Pakistan would have profound repercussions in the neighboring violence-prone Indian state of West Bengal, already shaken by the influx of more than three million refugees from the Pakistani Army's campaign of terror. Prime Minister Indira Gandhi is under mounting pressure to intervene to try to check this threat to India's own internal peace and integrity.

It is obviously in nobody's interest to allow the Bengali Spark" to explode into a major international conflict, one which might speedily involve the major powers. Nor is it wise to permit the situation in East Pakistan to continue to fester, inviting the gradual political disintegration of the entire subcontinent.

To deprive Tariq Ali and his like of their "big opportunity" it is essential that Pakistan's President Yahya Khan come to terms speedily with the more moderate Sheik Mujibur Rahman and his Awami League, which won an overwhelming popular mandate in last December's national and state elections. Such an accommodation with East Pakistan's elected representatives should be a prerequisite for the resumption of United States aid, except for relief assistance, to Pakistan.