INDIA has just made a sweetheart of an arms purchase, not its first, from the Soviet Union -- $1.6 billion in weapons on giveaway terms. The timing is especially scandalous. The Soviet Union obviously feels it is buying India's sympathetic and tolerant understanding of its invasion of Afghanistan. The contrast with the recent American military-aid offer of $200 million (at 11 percent interest) that Pakistan rejected as "peanuts" is, presumably, one that a smirking Moscow would like everyone to draw. On its part, India is acquiring yet more of the means to confirm its unchallengeable position as the dominant power of the Asian subcontinent. Prime Minister Indira Gandhi is showing again that she can deal in the international big leagues.

The new Indian-Soviet deal is bad enough. It not only further weakens the anti-invation consensus. It also is bound to push closer toward desperation a Pakistan already deeply fearful that India, with Soviet approval, is gearing up to wipe it off the map. The Indians deny having anything faintly resembling that in mind. The record is plain, however, that each major (and sometimes not so major) increment of arms on the subcontinent feeds the spiral that has already produced three wars. In regional terms, the latest package, unaccompanied by even a formal bow to the requirement of political conciliation, is more kerosene on the fire.

The trouble is that this particular Asian military package is not the only one tied up in the last few days. In Washington, the door through which China acquires military equipment from the United States has just been cracked open a bit wider. Washington is not, or not yet, selling arms to Peking, but it does plan to sell selected technology plus "non-lethal" items like air defense radars.The rational for the new steps is the Soviet invasion of Afghanistan, which has made the notion of containing Soviet power more urgent, and more saleable, and more swallowable by an adminstration that came into power with very different ideas.

The world of arms sales is practically seamless. The Kremlin invades Afghanistan. The Pakistanis then look to the United States for arms. India takes the occasion to go to Moscow; strategically, Indians divide into those preoccupied by Pakistan and those preoccupied by China. The Chinese, seeing the Soviet moves in Afghanistan and, no doubt, in India, arrive in Washington. The Kremlin, eyeing the Chinese . . . But you get the idea: Rube Goldberg could sketch it best.

The kworld is not coming to an end. But as the countries making up this particular cat's cradle narrowly pursue their separate national interests, they are losing increments of control over their common destiny. It is not possible for the United States alone to check the drift. That would be hard even if this were a vigorous administration early in its term of power. But neither is it possible forr the drift to be checked unless the United States takes a serious comprehensive approach to the politics of the region as a whole. Simple slogans about cooperation or, for that matter, about confrontation won't do the job.