THE NICARAGUAN GUERRILLAS, four blocks from the "bunker" housing President Anastasio Somoza, see the new American initiative as an attempt to deprive them of the fruits of their struggle. They are only half right. The administration is agitated by the prospect of a victory by guerrillas beholden to Cuba. But it is also stirred by the prospect of a continuing war. Its proposal (to the Organization of American States) for a broad-based transitional government, one assisted by an inter-American peacekeeping force, does brush past the more narrowly based provisional government that the Sandinistas wish to install. All the same, the American proposal, with or without the controversial peace force, provides a way by which the Somoza regime could be removed, a cease-fire reached and a democratic process set in train.

President Somoza, it is clear, is through, even if he survives the current battle. His writ extends no further than the National Guard's guns. The popular forces arrayed against him much more nearly represent the popular will. Americans had a rare opportunity to see for themselves the nature of his rule when the Guard murdered, on television, a respected American journalist, ABC's Bill Stewart. If it was a reversal of 46 years of cynical policy for the United States, which installed the Somoza family, to turn openly against it, then it was a reversal made unavoidable by the family's utter discrediting of any legitimate claim to rule. President Somoza's cries that Communists have instigated the attack on him and will profit from his fall ignore this central fact.

Still, the United States does not have to apologize for being apprehensive about the possible appearance, in a region ripe for further such revolutions, of a Cuban-type or Cuban-oriented regime - especially one that takes power in the heat of battle rather than in the cool of the election booth. There is reason to suspect that even those nations offering one or another degree of backing to the Sandinista-sponsored provisional government are doing so out of enthusiasms that do not reflect the more level-headed assessment of their own interests likely to be asserted after the battle. The Sandinistas, who have carried the brunt of the fight against the Somozas, should not be reluctant to test their support in the kind of internationally supervised polls contemplated by the American proposal. No doubt they would do well. They and their allies might even win, in which case the United States would have no choice but to accept the Nicaragua people's decision.