The Carter administration is moving hesitantly into a new phase in the Afghanistan crisis. To its political reprisals and military preparations it is adding a search for diplomatic ways to undo or at least limit the damage done by the Soviet invasion. It hopes the Soviet Union will see its self-interest in the same terms.

Well, it's worth trying, and not merely because jittery allies and some liberal constituents ask reassurance that Jimmy Carter has not overreacted.No realistic diplomatic stone should be left unturned. Yet neutralization, the idea currently being explored inside the administration and in Europe, shows some of the pitfalls of the diplomatic way.

Neutralizing Afghanistan sounds great: it promises the end of the Soviet occupation, the restoration of the nonalignment that Afghanistan ostensibly enjoyed before the trouble broke out, and the removal of a contentious place and issue from the great-power struggle. It would mean success for the old Carter policy of accommodating the Third World and for the new Carter policy of standing up to Soviet power: a diplomatic twofer.

But is it worth it to Moscow to try to turn the clock back to Dec. 26, the day before its Afghan pounce? By the most benign interpretation of the move, the Kremlin meant to clean up a mess in an area of its traditional interest. But in this event, neutralization, including a Soviet pullback, might cost Moscow precisely the control it crossed the border to acquire. Carter's proposal to replace Soviet troops with Moslem peacekeepers may seem only a backdoor invitation to the counterrevolution.

At the other extreme, suppose that either before or after the invasion the thought entered some Soviet heads that a position in Afghanistan provided strategic options in places further afield. In that event, neutralization might appear to be a plan to deny Moscow the very fruits for which its costly military operations was undertaken.

Neutralization, or a version of it, worked well enough in Afghanistan for 30 years, or 100 years. But it collapsed on Dec. 27. It is hard to see how it can be revived in circumstances in which only one of the two ultimate guarantors has usable power on the ground. Fond European wishes notwithstanding, Afghanistan is not Austria.

So, you may ask, if not neutralization, what?

The first task, I think, is to sort out diplomatic priorities. It is desirable to scale back and eventually remove the Soviet military presence in Afghanistan. But it is urgent to ensure that the crisis does not spread beyond Afghanistan. As it happens, one available key to both purposes lies in the military aid the United States is reportedly supplying covertly to the Afghan resistance.

The Soviets have at least two hardball responses they could make to American-suported resistance mounted from Pakistan. They could sponsor hot-pursuit raids into the guerrillas' camps. They could have their Afghan clients reactivate an old territorial claim, one that raises the question of Pushtun separatism and could conceivably lead to the dismemberment of Pakistan. The resistance is often presented as something noble, perhaps even a bit romantic, as something that raises the costs the Soviets must pay for their occupation. But it is heavy stuff. It could bring the United States under intense pressure to give meaningful assistance to the Pakistanis -- in conditions unfavorable to the American side. It could lead to a spreading of the crisis.

The whole matter of the Afghan resistance is bizarre. No credible suggestion has been made that any part of the opposition that brought in the Soviet troops had American strings. Clearly, the preponderance of the continuing resistance is entirely indigenous. Any American contribution has been slight and recent. But it has gotten into the public domain, and now it lies out there leading a certain whiff of legitimacy to Moscow's contention that it sent in its troops simply to deal with an "external threat" and "imperialist interference."

An agreement to ensure mutual respect of the Afghan-Pakistani frontier may now be to the point. It could help keep the Afghan crisis from spilling over the boundaries of Afghanistan and, over time, it could contribute to reducing the dimensions of Moscow's Afghan expeditionary force, the better to diminish any temptations to use that force elsewhere and, little by little, to let the Afghans breathe. Whatever Afghan operations the United States, or others, may be supporting must be measured against these purposes.

To some this will seem appeasement. To me it seems a judicious balancing of ends and means. At bottom, that, and not pulling rabbits out of hats, is what diplomacy must be about.