AS MISS NICARAGUA tearfully threaded her way down the runway last week, laden with 12 American Beauty roses and a promotional contract as Miss Universe, the curtain came crashing down on the regime which for nearly half a century has run the show in her home country. And although the violence emanated from Managua, most eyes looked to Washington as Carter faced his latest test of leadership in foreign police.

The President's position swung full circle since he backed the deadweight Shah in the showdown in Iran a few months ago. In an act of rare decisiveness, Carter made it clear to President Anastasio Somoza that despite his appeals, the only aid he could hope for from the U.S. was as a refuge.

Ironic in Nicaragua's case is that the U.S. participated in negotiations felling the government it had carefully planted there in 1934. That year, as U.S. Marine boats reluctantly pulled away from Mosquito Coast after 25 years of virtual control in the area, a U.S.-educated National Guard remained. That officer, Anastasio, "Tacho" Somoza Garcia, after nearly disposing of Nicaragua's President, established the iron-fisted dictatorship which he passed down to his sons, Luis and Anastasio Somoza Debayle.

"The U.S. position has always been to recognize countries, not governments," insisted a State Department official during the heaviest fighting last week. The U.S. has never flinched, however, at plunging into conflicts within the countries it recognizes, and it feels right at home in Nicaragua, a country intervened in militarily for years. Perhaps out of a fondness for the militia it trained and assembled, the U.S. negotiated the hardest with Sandinista leaders last week to preserve the National Guard, fearing the radical and Communist persuasion of some members of the Sandinista Liberation Army and ignoring the symbolic ties of the National Guard to Somoza's government. But these attempts were as unsuccessful as appeals to include more conservatives in the forming junta.

In fact, despite their efforts, U.S. officials even failed to keep the situation in Managua from disintegrating into the chaos that ravaged the city for about 36 hours before the Sandinist junta gained control. Soldiers rushed into and out of downtown office buildings. So hopelessly disorganized were both sides, that when a random officer of the National Guard wandered into in terim President Urcuyo's bunker seeking written permission for his son to leave the country, the President pounced upon him to serve as a liason between the government and the new junta. Within several hours, the officer managed to accomplish what neither the U.S., Sandinists, nor Urcuyo had been equal to: establishing communications between the groups, and setting up direct negotiations.

ALL THESE EVENTS point up the dwindling U.S. influence in an area where it once enjoyed nearly complete control through complaisant leaders. But U.S. withdrawal from its traditional position supporting Somoza, even though dictated by the determination of Nicaraguan rebels, is a fundamental step in the right direction, a basic prerequisite to reestablishing the trust of a people whose skepticism of U.S. motives towards its country runs in the blood, and with good reason.

For Nicaraguans, Somoza represented the U.S. economic exploitation which has overshadowed Nicaragua since the U.S. raced the U.K. for transition rights in the 1830s, and which continues today. Nicaraguans threw their own President, Jose Zelaya, out of office in 1909, because he had stirred up U.S. hostility when he told the U.S. that it would have to stop elsewhere for a site for the canal it planned to build. Zelaya refused to sign a treaty which he felt was unfairly advantageous to the U.S.

Since then, U.S. businessmen have managed to make do by exploiting Nicaragua's gold mines and controlling its benking industry. All brought to you through the courtesy of the Somoza government, which made exploitation easy. When things got hot, he declared all nine opposition parties illegal, including a tiny band of radicals who called themselves Sandinistas, and had their members arrested and tortured.

Observers protesting Carter's "back-stabbing" and confused over U.S. cooperation in removing from power a regime it established and funded for years should be silenced by the demonstration in Iran's case of the value of a promise blindly kept to a cruel despot without a realistic assessment of the state of the country.

Carter's administration implicitly admitted the error of the Somoza reign in its close negotiations with opposition Sandinistas and its insistence that Somoza and Urcuyo immediately hand over control of the country. In its obsequious eagerness to establish relations with the rising star of the Sandinistas, the U.S. dealt meekly with rebel leaders, saving heavyweight tactics for Somoza and his troupe. Deputy Secretary of State Warren Christopher informed Somoza that if interim President Urcuyo continued to bollix the transferral of power to the rebels by refusing to give up U.S. Characteristically, the U.S. approached the problem of Urcuyo's last stand as a business transaction, "he advised me that if the deal went through, I was welcome in the U.S.; if the deal did not go through, I was not...." reported Somoza.

U.S. reconstruction should not start in the rubble of a bombed-out country, but at the source, with an examination of U.S. foreign policy. The U.S. could try instigating more responsible policies than paranoically giving massive subsidies to the power-puffed, heavy-handed Shah. I could avoid alienating practices such as shoring up Pol Pot, (whose administration did not fall so much as it rotted out from beneath him) in an odious attempt to expiate the unforgivable acts of the U.S. relations with "non-priority" countries like Mexico, earning the resentment and distrust of yet another country when its reserves of oil suddenly turned a brusque President into a kneeling suitor.

The most chilling aspect of the Nicaraguan crisis is the sense of deja vu that hangs over the scene. As Pol Pot and Shah Reza Pahlavi were cast by the wayside, to be replaced with governments far worse, if imaginable, than their predecessors, and as Allende fell and his country experienced a similar fate, can Nicaragua expect to 'meet the new boss, same as the old boss," as The Who put despite State Department fears for the worse, is actually comprised mostly of businessmen and U.S.-educated professionals, including only two hard-core leftist guerillas.

PERHAPS IT IS FITING that two other members of the junta, Violetta and Joaquin Chamarro, are the children of the President who fell from power shortly before Anastasio Somoza's Debayle's father made his meteoric rise. But poetic justice will not sustain their newgovernment. If they succeed in their dream of becoming a social democracy, the U.S. will find it must account for its dealings there in the future. If not, the coalition could dissolve into another civil war.