Just how vital to American security are our military facilities at Subic Naval Base and Clark Air Base in the Philippines? And if I may follow up, Mr. President, are there acceptable alternatives?

So far, all we have is President Reagan's news conference statement the other day, that he doesn't know of any more important U.S. military bases. Before they are done constructing a new policy for the Philippines in the wake of the election debacle, both the president and Congress will have to address these questions more precisely.

It is all very well to talk about manipulating Filipino politics by cutting off military and economic aid. But U.S. aid is tightly connected to the U.S. base rights and to fighting a growing communist insurgency. The insurgency, in turn, thrives on conditions -- entrenched corruption, an inept military, economic stagnation and deep social grievances -- that won't go away quickly even if Marcos does.

What is at stake is nothing less than how the United States perceives its role in an immense and critical region stretching from Japan all around the rim of the Pacific Basin and down through the Indian Ocean to the Persian Gulf.

Even the People's Republic of China, with a shared concern over a hostile Soviet Union, would be nervous about the absence of a U.S. mlitary bastion in the Philippines. So we're not just talking about freedom of passage for oil tankers and U.S. warships through "choke points" or about fighting fantasy battles with an expanding Soviet naval force in the Pacific. We are talking heavy geopolitics having to do with "the projection of U.S. power," as a strategist put it, and the reinforcement of important U.S. political and commercial interests.

In that sense, the loss of Clark and Subic would constitute a significant U.S. disengagement from a region where it has had long and close ties with valuable allies -- unless a comparable U.S. military capability could be established elsewhere. Yet, with a few exceptions, notably Sen. Jim Sasser (D-Tenn.), congressional calls to cut off aid to the Marcos regime largely ignored the geopolitical considerations by ignoring the nature of the aid. It is, by mutual understanding, compensation (the Filipinos call it "rent") for the bases.

When we threaten not to pay the "rent," it would seem to follow that we have to be ready to contemplate not having the bases, if the threat is to be credible. In that spirit, Sasser pushed through an amendment last year that calls on the Defense Department to answer by March 1 of this year the question that the administration would rather not have to answer: How good are the alternatives to Clark and Subic Bay?

Sasser's hope is that the alternatives will look attractive enoughto suggest that the United States is not all that dependent on the good will of whatever combination of forces takes power in the Philippines. But my guess is that the case won't be persuasive. Previous studies have revealed a remarkable consensus among independent experts and across the political spectrum that only considerably inferior facilities, with far less satisfactory capabilities, could be established in scattered locations at a staggering cost of as much as $8 billion and with much heavier operating expenses than Clark and Subic.

That's pretty much what the Carter administration concluded after a study in 1979, when it was negotiating the current base agreement and Marcos was trying to raise the "rent" exorbitantly. A year later the Georgetown University Center for Strategic and International Studies concluded in its detailed report that Clark and Subic Bay were "simply irreplaceable." Literally, there's no argument. There's a flaw in almost all the alternatives (Thailand, Australia, Japan, Guam, Palau and Tinean). Either they're too far away from the potential action or they lack a local work force or port capable of handling aircraft carriers.

"Any way you try to do it," says one former high official in the Carter administration, "it would mean diminishing U.S. capabilities." The question is not whether the United States could not survive by making adjustments in its commitments or in its perceptions of its missions in Asia. The point is simply that substantial adjustments would have to be made. You cannot deal with the domestic politics of the Philippines without cranking very large geopolitical considerations into your calculations.