BIRNAM wood is creeping closer to the palace of the Lord and Lady Macbeth of the Philippines. And American policymakers still haven't decided exactly what to do about it. US intelligence estimates and diplomatic dispatches indicate that Ferdinand and Imelda Marcos have their gaze so fixed on manipulating their levers of power that they have underestimated the growing power of insurgents on the far left of the moderate Aquino-Laurel alliance.
At least one intelligence report postulates that if there is no change of course in Manila, radical-left forces could effectively control the country by 1989.
Presumably President Reagan's special envoy, Philip Habib, will be briefed on both this future threat and current vote fraud -- as Senate Foreign Relations Committee chairman Richard Lugar was before him.
But what can Washington do?
Gradually the United States has been learning how to help foster orderly change in societies it considers vital to its interests -- and to do so without going to extremes of either duplicity or blind allegiance. (The benchmarks of such extremity are  complicity in the removal of Saigon's Ngo Dinh Diem by assassination and  unqualified praise and support for Tehran's Reza Pahlevi up to and beyond his overthrow in a Jacobin uprising.)
In the case of President Marcos, Washington can legitimately exercise a lot of leverage without appearing to average Filipinos to be an unwelcome ``big daddy.'' The US is entitled, and many would argue is morally bound, to withhold economic and military aid. As suggested in Congress, such aid can be left in the pipeline but held in escrow until a clearly elected government is installed in Manila. American leverage also exists in the form of influence on the World Bank and International Monetary Fund, as well as on American businesses dealing with the Philippines.
Recent economic sanctions against Libya illustrate the weakness of such leverage. But that weakness was accentuated by the unwillingness of regional allies -- the major European trade partners of Libya -- to join in doling out the economic punishment. In the Philippine case, Washington would likely find its main regional ally, Japan, more willing than the White House to push for an orderly end of the Marcos era.
Japan, whose prosperity depends on its sea lanes, would be concerned if a regime susceptible to Soviet influence appeared on the east (Philippines) as well as the west (Vietnam) side of the South China Sea.
Mr. Marcos's major worry, like that of many an autocrat before him, is believed to be that the younger officers in his military might turn against him in the continuing confrontation with his election opponent, Corazon Aquino. Those officers and some of their seniors come in daily contact with relatives, friends, and neighbors whose opinions have been changing since the assassination of Mrs. Aquino's husband, Benigno Aquino. Large numbers of them have been trained in America and observed the benefits of orderly democracy. Under Marcos, they have seen increasing unrest, unfairness, and economic decline.
What Americans are witnessing is just another chapter whose plot is laid down in an equation as old as written history. It's not very original to cite the too-long postponed fall of the Bourbons in France as an example of that equation. But that well-worn case makes the point. Idealist reformers were supplanted by Jacobin extremists in Paris, just as the Kerensky reformers were overwhelmed by the Bolsheviks in Russia. That is the danger in temporizing too long on the Philippines.
Those who passionately cry that American leaders have learned nothing from repeated post-1945 lessons in this field are losing sight of progress. Look at a sampling of names that illustrate the point: Chiang Kai-shek, Diem, Holden Roberto, Somoza, Reza Pahlevi -- not to mention assorted Bao Dais, Farouks, Idrises, and Soustelles that show the US is not alone in wrestling with how to keep change from being dammed up and then breaking loose in an extremist flood.
America no longer seems prey to fratricidal arguments like that over who ``lost'' Chiang's China. As already noted, the White House no longer appears ready to go the extreme Diem assassination route. The US seems wiser now than to back an inept Holden Roberto in Angola instead of the Jonas Savimbi it now, two decades later, belatedly and awkwardly embraces. And Baby Doc Duvalier's exit indicates progress beyond the policy of hanging on to the limb after it has been sawed off, as in that marked the fall of the Shah in Iran.
Now we shall see if this combination of lessons can be applied with skill in the Philippines. Moral behavior and Realpolitik clearly coincide in this case.
Earl W. Foell is editor in chief of The Christian Science Monitor.