The United States has unwittingly employed double agents loyal to Cuban President Fidel Castro to conduct a number of ongoing and sensitive intelligence operations in recent years, a high-level Cuban defector has told U.S. officials.

The defector, Maj. Florentino Azpillaga, has outlined to Central Intelligence Agency debriefers a Cuban espionage capability far more sophisticated than was commonly believed, according to U.S. intelligence officials who spoke on condition that they not be named.

His disclosure of the double agents was said to have cast doubt on the quality of U.S. intelligence operations involving Cuban sources, which had been considered productive and of excellent quality.

It also has embarrassed an intelligence community already shaken by last spring's U.S. Embassy spying scandal in Moscow and the Soviet KGB's resulting mop-up of U.S. espionage operations there.

One official said that Azpillaga's disclosures may focus renewed scrutiny on the CIA's foreign counterintelligence capacity, which has been under congressional criticism for some time.

"A lot of people are hot under the collar about this," one official said. "We certainly underestimated the Cubans. We never realized that the operations we thought were so good were theirs all along."

It was not possible to establish the number of espionage operations that appear to have been compromised by the Cuban agents or whether the operations were inside or outside Cuba.

However, Azpillaga is reported to have told U.S. debriefers that an undetermined number of Cuban government officials, once believed by the United States to be secretly working for the CIA, were feeding the agency misleading or useless information prepared by the Cuban DGI, Castro's foreign intelligence directorate.

Officials said that Azpillaga recited the details of several supposedly successful U.S. intelligence operations employing Cubans, telling startled debriefers that the Cuban government, not the Americans, was in control.

"Several of these guys were polygraphed by us and passed," one official said of the Cubans employed by the CIA. The fact that they went undetected, that official said, is "poor tradecraft, poor counterintelligence. We were had."

Information from the compromised intelligence operations presumably was used by the CIA and the White House to analyze and direct U.S. foreign policy. Officials said it now must be reexamined and probably discarded.

Azpillaga, 40, is said to have headed Cuban intelligence operations in Czechoslovakia. He defected June 6 but did not surface publicly until this month, when Radio Marti, a Voice of America radio station, began beaming taped interviews with him to Cuba.

Officials said that he has proven "a very significant intelligence figure providing excellent information" since he slipped with a girlfriend over the Czechoslovakia-Austria border and sought asylum in the United States. The CIA is reported to be continuing to question him about his career.

One official, while agreeing that the double-agent scheme was a shock to U.S. experts, played down dismay over the slickness of the Cuban spy apparatus. "They {the DGI} are direct surrogates of the Soviets and the Soviets are the best. They {the Cubans} train with them. Why do you expect less?" he asked.