A high-level Cuban official today described U.S. reports that as many as 3,000 Soviet combat troops have been moved into the island as "deliberate fabrication" designed to "slander" Cuba while it is hosting the nonaligned movement summit conference.

Another source close to the Cuban Government said the U.S. charges made Thursday by Sen. Frank Church (D-Idaho) were a "maneuver directed toward presenting Cuba as interested in converting the nonaligned movement into a Soviet instrument."

Cuba made no official public comment on the charges. Diplomatic sources said it was believed that Soviet troops, in varying numbers, have been in Cuba for several years.

While neither confirming nor denying the charges, the Cuban source said, "These are things the United States has known for a long time."

"This is like the Migs," the Cuban said, referring to a flap caused by a leak in Washington last fall that suggested the sudden presence of the Soviet-made jet fighters in Cuba. The leak came as President Fidel Castro was in the midst of overtures to the Cuban exile community.

At that time, Cuba charged the United States with choosing carefully the moment to reveal information it had known about for some time, with a view toward embarrassing Castro at an awkward moment.

The issue of Cuban military allegiance to the Soviet Union, and charges by some delegates that President Fidel Castro wants to move the whole nonaligned organization toward the Soviet Bloc, have been discussed heatedly here during preliminary sessions leading to the meeting of heads of state that starts Monday.

Cuba defends its close ties with the Soviet Union as not violating the nonaligned guidelines that prohibit foreign military bases (the U.S. naval base at Guantanamo operates without Cuban permission) or membership in military pacts. Foreign policy must be based on peaceful coexistence and anti-imperialism.

Cuba maintains that its military relationship with the Soviet Union is inapplicable with the Soviet Union is inapplicable since there is no Soviet "base" here. Hence the question of thousands of Soviet combat troops here becomes an important one.

Whatever Soviet military personnel the United States may be referring to, a Cuban source said, they may be among the "thousands and thousands of Soviet advisers" in Cuba.

There is little doubt that the United States is more concerned about the current nonaligned summit in Havana than it has been about most of the previous five meetings since the organization was founded.

U.S. officials fear that is Cuba succeeds in getting the nonaligned members to agree to a harsh denunciation of the Egyptian-Israeli peace treaty, the impetus of such a condemnation may be reflected in the United Nations debate on the Palestinian question next month.

Although Cuba has declared that the nonaligned countries and the Soviet Union are "natural allies" against what is described as U.S. interventionism and colonialism, many of the other countries in the 94-member organization believe the Soviets should also be criticized, and avoided, as interventionist.

Leading the group opposed to the Cuban line is Yugoslavia, whose 87-year-old President Tito met privately today with Castro for several hours. One reported result was a Yugoslav decision not to contest a Cuban move excluding the ousted Cambodian government of Pol Pot from the summit.

While Yugoslavia and others strongly objected to Vietnam's role in installing a new, pro-Soviet government in Cambodia last winter, the unpopularity and brutality of the Pol Pot regime have made it difficult for them to support in public those who were ousted.

The likehood is that the Cambodian seat will remain empty throughout the summit, with neither government admitted.

But there is little indication the two leaders agreed on much else. One source said it was unlikely that Castro and Tito, as representatives of the two distinct currents within the movement, addressed the primary issue in any terms other than "political cryptography."

Still, representatives of both governments are actively lobbying other nonaligned delegations. While Castro has appeared in public this week only to welcome early arriving heads of state, an informed source close to the government said Castro has personally visited, and lobbied, a number of foreign ministers in their hotel rooms.

At the same time, members of the large Yugoslav delegation have been seen buttonholing other representatives in lobbies and hallways.

What has become a heated battle of words during a preliminary two-day foreign ministers' meeting escalated today when Yugoslavia began selectively circulating an alternative to the main summit document written by Cuba.

No public information was released concerning the substance of today's Tito-Castro talks.

The Yugoslavs have made no secret of their objections to what they describe as Cuban manipulation of the nonaligned movement -- primarily through the harshly anti-U.S. summit document written by host Cuba.