President Samuel K. Doe of Liberia has now released most, though perhaps not all, of the several hundred military men and politicians he locked up after an attempted coup last November. It follows, he appears to believe, that the United States should release the aid it had slowed or held up to focus his attention on matters of democracy and human rights, and that it should otherwise act to fix Liberia's troubled economy and his own tarnished image.

*But wait. Then-Master Sergeant Samuel Doe came to power by coup in 1980. He killed his repressive and corrupt (and elected) predecessor and came increasingly to mimic his political style. Last fall he finally held elections but won, it seems, only by fixing the count. Frustrated officers mounted another coup; it failed, and many were killed. President Doe, a high school dropout, detained a considerable number of real and imagined rivals -- including Ellen Johnson-Sirleaf, a Harvard-trained opposition figure who was charged with treason for, among other things, being "in a festive mood, showing joy and happiness" on the day of the abortive coup. Meanwhile, Mr. Doe had himself inaugurated under a constitution whose ample guarantees of civil liberties he was by then honoring mostly in the breach.

sk,2 The Reagan administration, like its predecessors, has tended to treat this West African country with an indulgence flowing from its history as a client state founded by freed American slaves. This has been especially notable in a period when Washington was leaning hard and often publicly on two somewhat similarly situated right-wing rulers in the Philippines and Haiti. In Liberia, the State Department has tended to keep its appeals for democracy and due process in a low key. The operating theory has been that working with the known quantity of President Doe is the best way to help Liberia sort out its problems. This means encouraging him to reconcile alienated Liberians and to swallow the medicine prescribed by the international bailout agencies.

sk The administration's critics see it practicing ''constructive engagement'' with Liberia -- a slighting reference to the besieged American policy toward South Africa. It is a criticism the administration cannot afford to ignore. The United States has a special exposure in Liberia. It needs a sure and strong hand.