IN ATTEMPTING TO isolate the Sandinista government in Nicaragua, the Reagan administration may be falling into a familiar trap. As events of the past week showed, the administration has trouble appreciating sensitivites arising from the national interests of its allies in the region.

U.S. pressure on its closest friends and neighbors in Central America to go along with its policy of isolating Nicaragua has led to a series of diplomatic flaps and embarrassments for the administration reminiscent of blunted U.S. initiatives in the Middle East, Western Europe and, earlier, in Southeast Asia. In this case, the U.S. policy toward Nicaragua has cut across the goals of such U.S. allies as Mexico, Guatemala and Honduras.

Illustrating the point is a National Security Council paper prepared for an Oct. 30 meeting of the NSC at which President Reagan presided. The paper, leaked last week, credits U.S. foreign policy with success in blocking efforts by Venezuela, Panama, Colombia and Mexico -- known as the Contadora Group -- to obtain early signing of a proposed regional peace treaty in Central America.

But the paper says problems remain in getting the "Core Four" countries -- Guatemala, Honduras, Costa Rica and El Salvador -- to agree on a position consistent with U.S. policy against Nicaragua, the fifth potential signatory.

It is apparent from the NSC document that these problems stem from the United States' persistent failure to recognize the role that national interest plays even in the most pro- American, anti-communist and economically-dependent Latin countries.

Central America is made up of six tiny nations. Guatemala, the largest, has a population of 6.5 million. Belize, the smallest, has barely 148,000 and belongs culturally and historically to the Caribbean. The populations of Honduras and Nicaragua hover near 3 million each. So minute are their economies (Costa Rica's gross national product is $3.7 billion) and so excessive their foreign debt (Costa Rica's totals $4.2 billion for a country of 2.5 million people) that they rarely make a move without looking over their shoulder to see whether Uncle Sam is scowling or smiling.

When the United States flashes a red light on a regional initiative, the outcome is predictable: Last September the Contadora countries and the Central American countries appeared to have reached mutual agreement on the draft of a peace treaty all parties would be willing to sign. But the peace talks came to a screeching halt after the United States signaled its displeasure.

While the Mexicans fume over the scuttling of their months of patient bargaining with the Sandinistas to keep them in the Contadora process (the NSC paper claimed credit for thwarting the Mexican effort), the NSC memorandum notes approvingly that some Contadora ministers "now concede that agreement (on the peace treaty) may not be reached for some months."

Mexico is not the only country affected negatively by the U.S. policy. In Honduras, rumors of coups and countercoups are everywhere, as increasingly large sectors of the military, the established political parties and a group of powerful industrialists rebel against the perceived sell- out of President Roberto Suazo Cordoba to the United States.

Honduras' traditional enemy is the Salvadoran army, and several high-ranking Honduran officers are known to have refused promotion because it involved serving in the despised military school that Suazo Cordoba allowed the Pentagon to set up in Honduras for Salvadoran troops. "First we train them, so they can come back and make war on us," said one such Honduran officer, "and then if the (Salvadoran) guerrillas should win, we will have bought ourselves a new enemy."

Now the United States appears to be contributing to tensions between Guatemala and Honduras as well by ignoring Guatemala's historic role as the preeminent voice in the region and promoting Honduras as its new best friend.

The Guatemalan response has been to side increasingly with Mexico and Nicaragua, who want to sign a revised draft of the Contadora peace treaty, and not a proposed counterdraft sponsored by the United States.

The NSC paper recognizes that "The uncertain support of Guatemala for the Core Four is a continuing problem. Guatemala's chief security concern is its guerrilla insurgency and the sanctuary that it has, until recently, enjoyed in Mexico. Mexico's removal of the border refugee camps . . . provide a strong incentive in pulling Guatemala towards Mexico in Contadora."

By its efforts to influence the outcome, the administration has undermined Contadora's main claim to legitimacy: that it is a peace initiative sponsored by Latin Americans who have only the interests of other Latin Americans in mind. In the process, the administration has also placed itself on the other side of the fence from one of its most influential and closest allies -- Mexico.

The administration of Mexican President Miguel de la Madrid is neither communist, nor leftist, nor anti-American. But just as Americans take pride in being citizens of this country, so do Mexicans take pride in belonging to one of the largest and wealthiest countries in the hemisphere. Mexico sees itself as a hemispheric leader, and tends to pursue a foreign policy that has the interests of Mexico, and not the United States, in mind.

For Mexico, as for Panama, another Contadora country, the idea of a regional war involving Nicaragua and the guerrillas of El Salvador and Guatemala against the rest of the area, with the United States using Honduras and Panama as staging areas, is intolerable. The only acceptable solution is to work out a treaty that will guarantee peaceful coexistence.

The United States might disagree with these positions, but the wording of the NSC memorandum reveals how sharply battle lines have been drawn. "Mexican and Nicaraguan representatives have been highly active but so far unsuccessful in efforts to obtain international endorsement," for the original revised Contadora peace treaty, the document says. Shultz "was direct in expressing our displeaure at Mexican conduct" at the United Nations General Assembly, it adds.

These circumstances point to three unsettling conclusions: First, that any negotiations for peace in Central America that do not rely heavily on U.S. backing have virtually no hope of success. Second, as long as the administration pursues a policy of isolating Nicaragua from its neighbors, diplomatic strategies designed -- like Contadora -- to reincorporate Nicaragua into the Central American community cannot rely on genuine U.S. support.

The third point is that the administration will have difficulty implementing a workable regional strategy for its friends and allies in Latin America as long as it fails to take their legitimate national interests into account, expecting them instead to adopt the United States' national interests as their own.