SOLDIERS OF the Liberian army broke into the French Embassy in Monrovia on Saturday and seized the hiding Adolphus Tolbert, heir apparent and eldest son of the president ousted in the April coup. This brazen violation followed repeated assurances by head of state Sgt. Samuel Doe -- assurances given to Liberia's West African neighbors and to a recent American mission led by Rep. William H. Gray Ill (D-Pa.) -- that the country's military government was heading back toward accepted ways. Its postcoup summary public executions of the old leaders, including president William R. Tolbert, had sickened many people who wished to be friends of Liberia and clouded their acceptance of the social revolution that accompanied the coup. The break-in at the French Embassy is bound to add to the costs, especially if the ruling sergeants fail to honor their pledges of due process for the captive Adolphus Tolbert.

But the embassy incident is not the oly sign of trouble. Two months after their coup ended more than a century of rule by an American-descended settler elite, the sergeants have failed to convey even to sympathetic Liberians just what their program is. Their evident enjoyment of the perquisites of power has raised doubts about their readiness to turn to civilian, let alone democratic, rule. Nor have the sergeants shown a sense of how to deal either with immediate debt and food problems or with underlying social and economic ills. Seeing an opportunity, Libya, Ethiopia and the Soviet Union are dangling offers of arms, cash and solidarity.

West Africans have their own interest in keeping soldiers in the barracks and foreign scavengers out of the region, and they have been working to settle the sergeants down. They have, for instance, so far denied them a part in regional economic meetings, even while counseling them intensively. On its part, the United States accepts a historical patron's role on account of the settler connection. But economic and strategic considerations have made the adminstration wary of the confrontations on human rights that Jimmy Carter's proclivities might once have brought about. When Liberian troops crashed the French Embassy, the United States cooled its Iran-connected concern for the involability of diplomatic premises and confirmed its protest to private words. The administration is relying on quiet diplomacy, too, and a discreet manipulation of the small available aid. The question remains: is the American approach so delicate that the sergeants are not getting the point?