IT IS HARD to watch Zbigniew Brzezinski and Clark Clifford tracking over South Asia -- the one sewing up the details of a substantial military (and economic) package to Pakistan, the other offering a new arms package including sophisticated guidance systems and "smart bombs" to India -- without feeling a little warning buzz of unease.

Yes, the Soviet invasion of Afghanistan has created a need for demonstrating solidarity with Pakistan -- as much to heighten deterrence by advertising the American connection as to strenghthen defense by providing more modern tanks and planes. And yes, any move to bolster Pakistan creates a political requirement to mollify India -- so that a policy undertaken to equip South Asia to deal better with external menace will not end up simply aggravating the tensions that have produced three wars between India and Pakistan in the last 30 years.

We know all this and you know all this and yet there is this uneasiness. Why? An awful lot is happening awfully fast. For three years, South Asia ranked relatively low on the Carter administration's list of international priorities. This had its reasons: the region has not been a conspicuous arena of American diplomatic achievement, and the United States had more pressing concerns elsewhere. If there was one major theme knitting together the administration's various approaches to the subcontinent, it was a deliberate, diligent though lamentably ineffective effort to divert both India and Pakistan from their respective programs to build nuclear bombs.

The Afghan crisis thrust upon the administration pressures to act promptly and surely in a region it had pretty much set to one side. The first thing it did was to suspend the separate punitive actions it undertook against both Pakistan and India on account of their nuclear programs. The next result, the one being carried forward by the Brzezinski and Clifford missions, was to enter into new discussions on regional security.

Where it will come out is hard to say. But the evident fact is that the United States has removed whatever inhibitions its previous nonproliferation policy placed on the nuclear development of these two rivals, and it is helping them conventionally rearm. It is doing so in a larger political context in which Pakistan openly, even rudely, questions whether the United States is a reliable and adequately generous patron, while India, whose vastly superior military forces come mostly from Moscow, openly pursues a strategy of more or less accommodation with the Soviet Union. The kinds of arms the United States is providing, moreover, seem to fit the traditional preoccupation of the Indian and Pakistani general staffs with each other.

We recognize that it is too much to ask that the United States dot all i's and cross all t's before trying to help brace a shaky region flanking the crucial Persian Gulf. At least, however, the policies that Mr. Brzezinski and Mr. Clifford have been elaborating should be closely examined. The security issues and their political implications obviously deserve attention. But how does the administration now intend to deal with the specter of the spread of nuclear weapons on the subcontinent? Surely the tension in that part of the world can only reinforce the belief that the last thing needed there is nuclear weapons. The crisis, in other words, cuts both ways. The administration must be able to show that in order to meet urgent short-term requirements it is not abandoning objectives that were, and are, essential and right.