TO UNDERSTAND just how perverse things are in the Philippines, you have only to reflect on the (fair and accurate) headline on a story in this newspaper the other day about how President Ferdinand Marcos intends to deal with his political opposition. It's not that in his frustration he is warning of a coup or some other use of military authority in order to consolidate his and his wife's and his cronies' exalted position. What the headline said was: "Marcos Threatens Early Election." The story went on to explain that in raising the prospect of a snap election the 67-year-old Marcos apparently was gambling that opposition disunity would keep him in power.

There lie the irony and the true difficulty of the situation in the United States' colony-turned-ally. President Marcos has misgoverned the Philippines badly, abused power for the personal gain of his family and friends, and helped create a communist- led insurgency that appears to be gaining steadily in the countryside. He has managed to turn the American strategic and sentimental attachment to his country into a bulwark of his personal rule, notwithstanding efforts by successive U.S. administrations, including in its fashion this one, to steer him toward reform and, that failing, to put a bit of daylight between Washington and the man in Manila.

But at the same time Mr. Marcos has exploited the forms of democracy, playing divide-and-conquer politics and appealing deftly to the people's complex and confused feelings toward the United States. When he fights dirty, he wins, and the opposition curses him. When he fights clean, or pretty clean, he looks like a winner too; for this, the opposition cannot forgive him.

So what is the United States to do in order to prevent one more right-wing friend from going down the drin and carrying the American interest with him? Or rather, at this late date, how can the United States nurse along reform and change in a way that will avoid destabilizing the country and opening the door to a communist takeover?

Perhaps Washington cannot do too much more than it is already doing. This includes the administration's emphasis on democratic process, economic stabilization, good government and effective counterinsurgency, and the congressional effort to redirect aid away from the military and toward civilian needs.

But the Filipino democratic opposition has its own responsibility. Its leaders decry the tendency of President Reagan to pose the Philippines' choice as either Ferdinand Marcos or a communist deluge. Yet they do not pull themselves together in order to create a viable third option. They are the ones who make it possible for President Marcos to "threaten elections."