President Reagan's pronouncement on this week's election in the Philippines set forth what looked like a settled, straightforward policy. The United States will weigh in against assorted Filipino perils with "significantly" increased economic and military aid over the next five years. But it will do so only if the outcome is "credible" to the Filipino people and if "whoever is elected" makes "fundamental economic, political and military reforms."

There is really only one catch that I can see: Never mind whoever is "elected," incumbent President Ferdinand Marcos can be counted on to count himself in. Few doubt he has the resources to declare himself the winner over Corazon Aquino, who inherited the leadership of the opposition after her husband was assassinated in 1983. In that event, there is no policy.

Worse, those two monumental "ifs" attached to the president's offer guarantee a rough-and-tumble struggle within the administration and between the administration and Congress over new policies in the Philippines. Just to begin with, an election conducted under a Marcos government will not be accepted as "credible" by the significant numbers of Filipinos who have flocked to Aquino's support. That's because Marcos himself is not credible. There lies an irony in his strategy of a quick election to invest his regime with the trappings of democracy. In large part as a consequence of revelations during the campaign, Marcos grows less appealing by the day.

The tight focus on his regime and rule has confirmed what was already known about the corruption and repression. It has revived the issue of his military's involvement in the assassination of Benigno Aquino. Only a Marcos crony who was chairman of an investigatory commission departed from the finding of the other four members that a conspiracy to kill Aquino ran up the military chain of command to another Marcos crony, Gen. Fabian Ver, the armed forces chief of staff.

Now we also have new evidence that Marcos' war record was a concoction. Reports multiply that he and his wife, Imelda, have been plundering the state for personal gain. He has campaigned with the light touch of a mugger.

Marcos would have a credibility problem then, even with little evidence of foul play. Tension is already high. Violence is already breaking out. A post-election uproar is assured. And it won't be just a matter of how much the Reagan administration chooses to make of it. Even if it could find it possible to turn a blind eye, congressional overseers on the spot, including Senate Foreign Relations Committee Chairman Richard Lugar, are likely to come back with a jaundiced view.

As to that second presidential "if" -- the one having to do with reform -- the record speaks for itself. If Marcos was either willing or able to carry out "fundamental" reforms, he would have long since yielded to pressure from successive U.S. administrations to throw out corrupt officials and promote a new generation of military leaders with the will and skill to deal effectively with the communist guerrilla forces.

This has brought some U.S. policy makers increasingly to the conclusion that they are demanding the impossible, that they are asking Marcos to dismantle his power base, and that the only realistic course is to stop pretending that the United States can work with him. Some would apply pressure with only modest leverage from a relatively modest aid program to persuade him to agree to a timetable for a phased surrender of his power. Others would simply stand back and count on his poor health to phase him out. There have even been reports that there is an administration "cnsensus" for such a course of action after the election.

But that composition is vigorously denied by Secretary of Defense Caspar Weinberger. When I put it to him the other day, his answer was that if there is a consensus, "I'm not part of it." For Weinberger the proper analogy is Iran, where, he believes, the Carter administration's push for reforms contributed to the downfall of the shah and his replacement by a far more repressive regime.

By this reasoning, the proper course for the United States is not to rock the boat but to take Marcos for what he is and help him in his struggle against the communists for the sake of the Subic Bay Naval Base and Clark Air Force Base. That both are irreplaceable and vital to U.S. security is not in serious dispute. The argument waiting to break out is over the best strategy of safeguarding these security assets.

Here lies the true analogy with Iran. Carter's policy was never completely one thing or another. Rather, it was victimized by divisiv and debilitating debate, in that instance between the White House and the State Department, until it was too late. Assuming that the experts have it right about the election outcome, that is the immediate prospect in the case of the Philippines. When the secretary of defense is not a part of a policy consensus having to do with vital U.S. security interests, there isn't a consensus.