BY ALFONSO CHARDY
Herald Washington Bureau

WASHINGTON ------- The United States ordered the expulsion Tuesday of two Cuban U.N. diplomats, accusing them of conducting "hostile intelligence activities" against the United States.

The two men were given 48 hours to leave the country, the U.S. Mission to the United Nations said.

In Washington, State Department spokesman Alan Romberg said the diplomats - Rolando Salup Canto, third secretary, and Joaquin Rodobaldo Penton Cejas, an attache - were told to leave the country because "they were accredited to the United Nations for the purpose of engaging in diplomatic activities [but both] had been engaged in hostile intelligence activities aimed at the United States in blatant violation of their privileges" as foreign diplomats.

The Cuban mission "firmly" rejected the American allegations and insisted that the diplomats had performed their duties "in conformity with their privileges of residence" at the U.N. headquarters in New York.

Romberg and other administration officials refused to provide details about the activities of Salup and Penton that provoked the expulsion.

"What they were doing, we know, was of a very sensitive nature and is still being investigated," an administration official said. He suggested that two diplomats may have been traveling around the United States conducting intelligence on behalf of Cuba.

The official, who requested anonymity, said the Cubans were not involved in any operation within the Cuban exile communities in the United States, a charge often used against Cuban diplomats in the past.

At the State Department, Romberg said that because of U.S. policy of "not disclosing or discussing" intelligence matters, he could not reveal the exact charges against the Cubans.

"Suffice it to say that those officials engaged in hostile intelligence against this country," said Romberg. "The illegal activities of these Cubans have been blatant and directed against this country. They are a serious matter."

The Cuban mission, the fourth largest at the United Nations, has a record of "continuing abuse" of residence privileges, Romberg said.

Salup and Penton are the fifth and sixth Cuban diplomats expelled in the last three years.

Romberg listed the others as Ricardo Escartin of the Cuban Interests Section in Washington, expelled in 1981; Mario Monzon Barata and Jose Rodriguez of the Cuban U.N. Mission, ousted in July 1982; and Juan Bandera Perez, also of the U.N. Mission, kicked out last August. All four were accused of "deliberate violations of the Trading With the Enemy Act" and Escartin was also identified as involved in intelligence-gathering activities.

Monzon and Rodriguez allegedly tried to buy American communications and electronics equipment for illegal shipment to Cuba.

The announcement of the expulsions came as the State Department said that it had denied a visa for Julio Garcia Espinosa, Cuba's vice minister of culture, to attend a film festival in Los Angeles.

Romberg said the State Department had a "long-standing policy" of denying visas to Cuban government and Communist Party officials seeking to enter the United States for purposes other than conducting bilateral relations or attending international meetings.