How unnatural, when you think about it, that Indira Gandhi, prime minister (again) of India, had not formally visited Washington in more than a decade. There are reasons, but they are petty and should not have been allowed to stand in the way of a high-level dialogue that ought to be routine.

India, as people always say, is the world's largest democracy--the example and practice of democracy in Indian economic and social conditions is of immense political value, as well as great sentimental satisfaction, to the United States. As the strongest country in the Asian subcontinent, moreover, India is the natural leader of regional efforts to diminish tensions and exclude the hostile influence of foreign powers.

On the face of it, Indira Gandhi and Ronald Reagan are not the likeliest of international chums. Their encounter, however, had been preceded by a good deal of heavy thought on both sides concerning the possibilities of expanding or emphasizing the common ground between two nations that will always have their deep differences.

It is suggested that the arrival of Soviet forces in Afghanistan has given Indians a fresh appreciation of the advantages of an easier relationship--certainly not a strategic alliance--with the United States. Similarly pragmatic considerations have widened the openings for free enterprise in India. On the American part, there has been a welcome readiness to look beyond superficial irritations and ideological disparities in order to bring Indian-American relations up toward the level required by the intrinsic weight of the two nations.

Philosophically, the Gandhi brand of nonalignment clashes with the Reagan brand of containment. Practically, however, Mrs. Gandhi can see that nonalignment has not kept or gotten Soviet troops out of Afghanistan and that, as a result, India's rivals in Pakistan have gained a new and, to her, disturbing standing in Washington.

Philosophically, the Reagan brand of free-enterprise development clashes with the Gandhi commitment to a mixed economy heavy on the socialist side. Practically, however, Mr. Reagan, while remaining cool to India's reliance on U.S.-backed concessional loans, has relaxed American objections to India's pursuit of large loans at the International Monetary Fund. Where there's a will, there may be half a way.

In one area of semi-accommodation, however, we see a cause for real complaint. The diplomats, thinking to eliminate a major source of bilateral trouble, attempted to address the long-running dispute over the supply of American uranium fuel to the two American-built nuclear power reactors at Tarapur. The result, however, is extremely troubling.

The United States will make sure India gets the fuel, from France: the American nuclear nonproliferation act had kept Washington from shipping fuel to India because not all of India's nuclear facilities have been placed under international safeguards. In return, India--well, India apparently gives nothing. The United States says India must ask its permission to reprocess Tarapur's used fuel--that is, to extract from it plutonium, a bomb material. Mrs. Gandhi, however, says India has not agreed to that at all.

We do not wish to spoil the general mellowness. But the fact is the administration has given away the nonproliferation store. India is not any country. It is the one country in the world that has diverted peaceful nuclear materials, including American heavy water, to explode a bomb, which it calls a "peaceful nuclear device." And now the administration is going back to nuclear business pretty much as usual.

Yes, there are political reasons to get the Tarapur dispute out of the way. Yes, India is not the only foreign country to take advantage of the administration's misguided relative indifference to the risks of plutonium. But this is one area where the wrong common ground was found.