The Reagan administration will be making a serious mistake if it does not make the Philippines its list of winter-book favorites for 1986's Crisis of the Year. Wagering on the worst theory of the case, and acting accordingly, offers the best hope of being proven wrong.

The worst theory of the case rests on evidence all too common to our postwar experience: a growing communist insurgency; valuable if not vital strategic "assets"; a politically repressive regime; a crumbling economy and a corrupted society; an aging, ailing, authoritarian leader trading heavily on the reputation of old friendship and alliance with the Americans; a weak and divided opposition holding out only the most forlorn hope of delivering the country to democratic ways. And, yes, there is eventhe prospect of an "election" to lend a measyears of government by President Ferdinand Marcos. Bitter campaigning is under way.

By now, you will have recognized bits and pieces of assorted sad analogies: Iran in the last years of the shah, Nicaragua in Somoza's last years; Vietnam in the period just before the downfall of Ngo Dinh Diem. In each instance, the United States was confronted with agonizing choices. In each case there was the same fundamental confusion when we spoke of "friends" -- the confusion between leaders and regimes congenial to our immediate purposes and the nations and/or peoples over which they presided.

There was the same noble talk of promoting The American Way, of advancing human rights, of elections and all the rest in nations where the stage was simply not set, either institutionally or traditionally, for easy revolution to democracy, American-style.

In the Philippines, there is a democratic tradition -- an American bequest in 1946 after 48 years of colonial rule. There is also a genuine friendship and there are business connections as well. U.S. security interests in the Pacific and westward to the China Sea and the Indian Ocean depend heavily on access to the naval base at Subic Bay and the Clark Air Force Base. Those installations are fixtures that even Marcos' opposition would, for all its campaign talk, be unlikely to remove, not least because of the 5 percent of Philippine GNP that they generate, together with generous U.S. military and economic aid.

But the appearance of promise in the February elections is deceiving. The roots of Marcos' power run deep into the military and into the economy. His leading opponent, the widow of Begino Aquino, has the appeal of martyrdom (her husband was the opposition leader), but is the first to say she knows nothing about the job she seeks. It is widely accepted that, one way or another, Marcos will not allow himself to lose.

It is at this point that you have to look to the American contribution to the problem. Unlike past situations of this sort, there is extraordinary agreement on the extent of the threat. Administration officials have confidently predicted "civil war on a massive scale" within three to five years at the hands of a growing communist military force. The only difference of opinion is with Marcos (and this has a familiar ring), who finds it convenient to boast that he can crush the communists within a year, without undertaking any of the military, economic and social reforms that U.S. officials unanimously agree are imperative.

This American consensus on the communist threat -- ranging from Sen. Paul Laxalt (R-Nev.), the president's special emissary, to Marcos, to Rep. Stephen Solarz (D-N.Y.), who is chairman of the House subcommittee responsible for the region -- distinguishes the Philippines from, say, Iran or Vietnam.

True, the administration has let it be known that it is looking for alternatives to the Navy and Air Force bases. But such talk is mostly for the effect this might have on Marcos. Estimates of the cost of alternative sites at Guam or elsewhere range from $2 billion to $8 billion. In any event, no alternative would serve U.S. strategic interests as well.

But there are distinctly familiar and debilitating differences of opinion over how to handle Marcos -- exactly the same sort of liberal- versus-conservative argument that compounded policy making for Iran, Nicaragua and Vietnam. It comes down to three choices: Sticking with the devil we know, Marcos, and risking going down with his ship; actively intervening in an effort to replace him with something better, the tactic that failed so dismally in Vietnam with Diem; or somehow exercising U.S. leverage to bring about an orderly, phased transition, with Marcos agreeing to hand over power to whatever forces seem most likely to be able to cope with both the communist insurgency and the economy.

The last course is the only one that offers much hope. That it is also the most difficult course is only a measure of the gravity of the crisis now building in the Philippines. The longer the rule of Marcos drags on, the likelier it is that the Philippines will fulfill the worst -- soon enough, if not in 1986.