Perhaps because religion is the opium of the masses it is also a convenient tool of politics.

That, at least, is the lesson of the recent history of the Indian sub-continent. From the start of this century, Indian and Pakistani politicians have exploited Islam, Hinduism and Sikhism to advance their own causes. These are as varied as they are unchanging: India's freedom movement; the birth of Pakistan; the struggle for "Khalistan"; General Zia's need for legitimization in Pakistan; or a hapless quest by Rajiv Gandhi to boost his popularity.This month Salman Rushdie's "The Satanic Verses" fell into that trap. In Pakistan, opposition politicians defeated by Benazir Bhutto and resentful of her position as Prime Minister organized demonstrations against the book's forthcoming American publication.

As a modern Westernized woman, Bhutto is secular in her outlook. But she has constantly countered the charge that Islam does not permit a female head of government.

Consequently, demonstrations of Islamic fervor are awkward to handle: If she ignores them she can be accused of belittling Islam; if she pays undue attention she may encourage the very fanaticism which already threatens her premiership.

After riots in Pakistan, it was the turn of opposition factions in India's Moslem majority Kashmir state to show their mettle.

There the chief minister, Faroukh Abdullah, is a British-trained doctor whose wife, Molly, is English. He is also a friend of Rajiv Gandhi. As a secular politician he is vulnerable to fanaticism.

The organizers of the Srinagar riots knew he would be embarrassed by their success. As a Moslem he could hardly defend the book. As an Indian he could hardly condemn the riot. That would mean Moslems Muslims in Pakistan were more free to express themselves than their co-religionists across the border.

Thus what happened in India and Pakistan was only at one level a demonstration against the supposed blasphemy of "The Satanic Verses." Deeper down it was domestic politics by another name. The Rushdie book was just another stone in the opposition's sling.

However, because it sparked off a religious issue - and one that touches millions - it has taken on an independent life. Pakistan has now called for a worldwide ban and threatened a boycott of Penguin, the publishers. But the irony of Bhutto, an Oxford and Harvard graduate, supporting censorship is lost on her people.

Bhutto's plight is mirrored by Rajiv Gandhi's similar fate. Educated at Trinity, Cambridge, and married to an Italian, he admits to agnosticism. In 1984, on becoming prime minister, he acknowledged the need to separate religion and politics. But no more.

It was against this background that the demand to ban Rushdie's book was voiced in India last October. The fact that it came from a second-tier opposition politician who had neither read the book nor a review hardly mattered. The issue was interpreted in terms of Moslem votes and the request granted.