Offering an impassioned defense of his country's honesty early yesterday, Cuban President Fidel Castro told American interviews that "brutal" U.S. charges of Cuban involvement in last month's Zaire invasion had undermined strong "possibilities for progress" in Cuban-American relations.

The tone of the dramatic post-midnight interview was one of hurt as Castro once more denied that his country gan incursion.

In an often eloquent preseutation, Castro stressed that the American charges were an insult to him and came precisely at a moment when the United States had made "just and constructive" moves toward Cuba.

The interview at Havana's Palace of the Revolution marked the Cuban leader's first public response to those charges and more direct accusations later made by President Carter that his troops in Angola trained and equipped the katangan secessionist soldiers that invaded Zaire.

Speaking in a subdued voice that occasionally rose as he repeated phrases for emphasis, Castro clearly intended his two-and-a-half hour statement as a direct refutation of the charges and a message to the U.S. government.

In answer to administration charges that he has lied about Cuban involvement, Castro said he had asked himself. "How am I going to tell a lie to Mr. Vance, when he has had a constructive . . . respectful attitude to the problems" between Cuba and the United States.

"How am I going to tell him a lie? How would I lie to (U.N. Ambassador) Andrew Young, who has been respectful and kind to us? How would I lie to George McGovern, who has been interested in improvement of relations with Cuba."

"But in addition," Castro asked, "how would I lie to Mr. Carter?"

The answer, Castro said, was that he had not.

"We may be private about some things," he said. "We may be discreet. But we never have lied. We have never made use of lies as an instrument of politics."

As his vie presidenc, Carlos Raphael Rodriguez, had done in a speech before the United Nations two weeks ago, Castro said he thought "Carter is an honest man. I think that Carter has been caught up by these deceits and lies." But, Castro noted, "Carter has an opportunity to find out the truth and to rectify the situation.

"I think that Carter has been confused and deceived," he said. "Everything will be known sooner or later. History will prove some day that we were telling the truth and that the charges against us were really false."

Castro describes the "so-called hard policy, the policy of threats, the policy of pressure," which he said the United States has used as "a serious, tremendous . . . irresponsible mistake." That policy, Castro said, "already has a name and a last name. It is (national security advisor Zbigniew) Brzezinski's policy."

The lie told against Cuba, he said, "is not a half lie. It is an absolute, total, complete lie. It is not a small lie, it's a big lie. It is not a negligible lie, it is an important lie."

The lie, which he said was " manufactured in Brzezinski's office" was intended to "provide a pretext of justifying the U.S. intervention and the intervention of the NATO powers in Zaire;" to manipulate U.S. public opinion and to pressure the U.S. Congress to "lift restrictions established on subversive activities by the CIA."

Castro also said that although he had no intelligence information preceding the raid he had heard rumors of it as early as February. he said that he had sent a message to Angolan Premier Agostinho Neto in which he explained all the problems that would result from any new action of the Katangans and that "our view was to prevent it at any expense."

Neto fully agreed with him, Castro said adding: I know he instructed his people to speak with the Katangans."