Blaine Harden's Dec. 4 article "Yugoslav Aide Threatens Separatist Republics" raises these unsettling questions: Amid the tidal wave of democracy now sweeping Eastern Europe and the Soviet Union, can Yugoslavia be regressing to Stalinism and communism? Is it possible that the defense minister, Gen. Velkjo Kadijevic, a Serbian, along with his other generals, can be allowed to form his own political party and then threaten to crush the democratic independence movements in Slovenia and Croatia? Sadly, it's all true. As Mr. Harden points out, Yugoslavia is disintegrating, and it's not difficult to understand why.

Yugoslavia, created in 1918 after World War I, was an experiment borne of many Slavic liberal-minded scholars and politicians. Unfortunately this idealistic pan-Slavism quickly gave way to the realities of Serbian hegemony, first between the two wars through a brutal Serbian monarchy, and then after World War II via Serbian domination of the Yugoslav Communist Party and its instrument, the Yugoslav Army. Today Yugoslavia is still largely controlled by the (Serbian) Communist Party and, as Mr. Harden points out again, its military, whose officers are more than 60 percent Serbian. Naturally these two establishments have the most to lose if democracy prevails, and Slovenia and Croatia are allowed to seek either confederation or complete independence.

Gen. Kadijevic and his new party, The League of Communists Movement for Yugoslavia, don't really seek the preservation and unity of Yugoslavia for altruistic reasons. If they did, they first would have called for the demilitarization of the heavily armed Serbs in Knin, Croatia. No, what this general and his Serbian backers truly desire is the preservation of a society that the forces of democracy will eventually overcome. And must overcome.

ANTHONY MARGAN Alexandria