A private, late-night session of two dozen nonaligned nations abruptly disintegrated Thursday when Cuban President Fidel Castro applied to those governments who disagreed with him one of the worst epithets one Third World member can hurl at another -- the Spanish equivalent of "imperialist stooges."

But while Castro's denunciations may carry the substantial weight of his personal presence, the Cuban leader has no monopoly on revolutionary rhetoric here.

Communist or capitalist, president, prime minister or king, few of the leaders meeting here for the sixth nonaligned summit have abstained from liberal use of the code words for what has emerged as the No. 1 nonaligned enemy -- the United States.

Each speech includes the litany of things the movement is against -- imperialism, colonialism, neocolonialism, racism (meaning ties with South Africa) and Zionism (meaning ties with Israel). One doesn't need a jargon dictionary to know whom they're talking about.

Still, there is a certain style of delivery that separates the pros from the amateurs, and many of the more moderate governments represented here haven't completely gotten the hang of it.

Following Thursday night's confrontation with Castro, those who disagreed with Cuba on the subject at hand -- the question of who holds legitimate title to the government of Cambodia -- addressed a protest letter to the Cuban Foreign Ministry.

"We have the honor to refer to the meeting . . ." it began. "We strongly protest . . ." it ended.

Such mild noninvective appears to go nowhere here and, as one of the 16 signers including Senegal, Singapore, Somalia, Yugoslavia and Gabon among others, explained, the issue was lost because they were no competition for the militants.

"For the first time in my life," one of the losing delegates said dolefully, "I know what it feels like to be a Third World dissident."

Continuing with the language of the nonaligned, the word hegemony is usually interpreted as referring to the Soviet Union. Among the infinite subtleties that characterize speeches here, one learns to watch for a mention of the evils of "hegemony" as a possible sign of someone who is soft on "imperialism."

At the same time, the word "bloc" has taken on great significance. Blocs usually refer to the West -- the United States -- and the East -- the Soviet Union. Since Cuba tends to view the Western bloc as an enemy and the Eastern bloc as a friend, it avoids wholesale condemnation of "bloc rivalry" and rarely uses the word.

Yugoslavia, however, is hard-line antibloc.In his Tuesday speech to the summit, Yugoslav President Tito made several mentions to that effect, and nobody had any trouble figuring out what he was talking about.

Cuba appears to have had the last word, however. In an article appearing today in Granma, the Communist Party newspaper, titled "The Lament of a Yugoslav Journalist," it referred to an article published recently in Politika, a Yugoslav paper.

The article, Granma said, complained that "the president of Cuba" in his Monday speech opening the summit "mentioned neither blocs nor bloc politics, nor did he mention the nonaligned view that rivalry between the blocs is a permanent source of the greatest dangers to world peace."

Granma, which has a certain monopoly on public information by being the only paper distributed here each morning, quickly put the Yugoslav in his place.

"According to observers," it said authoritatively, "this opinion radically contrasts with the interpretation given here by the leading heads of state, governments and liberation movements in countries where an even greater danger exists." There was no need for Granma to spell out what that danger was.

CUBA APPEARS to have won some converts through its forceful handling of the summit. Not the least of these converts are many of its Latin American neighbors. With 11 Western Hemisphere nations belonging to the nonaligned movement -- four added just this year -- Cuba has taken the lead here and the other Latin and Caribbean states have more or less followed.

For both Nicaragua and Grenada, following revolutions and the establishment of new governments, the establishment of official relations with Cuba has been considered a way of proclaiming their independence from the United States.

In other parts of the world, Cuba today announced newly established diplomatic relations with Jordan and Rwanda.

While summit hosting has given Cuba new access to other governments, it also has allowed the Cubans at least temporarily to limit the access representatives of the Western bloc have to nonaligned delegates.

At least five European countries and the United States have sent their nonaligned specialists here to observe the summit and try to make their influence felt on issues they are concerned about.

Their conracts have had to be outside the conference centers and villas provided visiting heads of state since the Cubans have not issued them the credentials necessary to enter.

At the same time, the specialists are charging that the Cuban government has followed them and attempted to intimidate those delegates seen talking to them.

Thus the specialists are largely reduced to hanging around in the lobbies of hotels housing lower level delegation members, trying to attract the attention of a friendly face as delegates rush in at night.

Sometimes, even that doesn't work. One Westerner sat last week waiting for a particular Asian, who had taken the day off to visit the beach, to enter. He finally came in just after midnight.

The delegate looked surprised, nervous and unwilling to be seen with him as he approached with his hand outstretched, the specialist said.

Fumbling with an excuse and looking around in a panic, the Asian sputtered, "Oh, no. I can't talk to you now. I've still got sand on my body." He ran for the elevators."

MANY JOURNALISTS covering their first nonaligned summit, at least among the Western press, were awestruck at the thought of being close to so many heads of state -- more than 50 are here -- and anticipated scores of the kinds of interviews most only dream about.

The truth, however, is that the segregation of the Third World mighty from the imperialists also appear to include journalists.

What gradually has become clear during the five-day summit is that not only the Cuban hosts, but most of the leaders themselves have no intention of being caught outside carefully prepared self-images.

Thus, although a number of the heads of states have offered news conferences, little earth-shaking news has emerged.

Typical was a conference offered Friday by Vietnamese Premier Pham Van Dong, an agreeable man who punctuated his answers with a number of giggles.

Asked whether improved relations between China, another non-aligned enemy to many, and the United States were a challenge to the movement, the self-assured president offered a succinct reply.

"The Chinese have been defeated," he said. "Imperialism has been swept away by history. Any more questions?"