A top Angolan leader yesterday ruled out talks with U.S.-backed anticommunist rebels and warned that the worsening conflict between South Africa and neighboring black African nations makes the withdrawal of Cuban troops more difficult.

Following a two-hour meeting with Assistant Secretary of State Chester A. Crocker on Thursday, Pedro de Castro Van Dunem, second-ranking member of the Politburo of Angola's ruling party, gave no indication he had made much progress toward persuading Washington to establish diplomatic relations with his government.

In an interview, he seemed to indicate a widening divergency of interests between his government and the United States, and little hope for improvement of relations.

"The basic interest here {in the United States} is withdrawal of Cuban troops and everything is conditioned on this," Van Dunem said.

The State Department had little to say about Crocker's meeting with a top official of a government that Washington refuses to recognize. Spokeswoman Phyllis Oakley said the two sides discussed "the full range of Angolan-U.S. issues," including the administration's efforts to gain a Cuban troop withdrawal and arrange for the independence of South African-administered Namibia.

She warned against interpreting the resumption of U.S.-Angolan talks over these issues as an indication of movement toward diplomatic relations.

Van Dunem, on his first trip here, said Angola is interested for both economic and political reasons in seeing the Cubans -- estimated at 37,000 by the United States -- leave, and would order them to go "as soon as conditions permit this." But he said the military situation in southern Africa is steadily deteriorating because of South Africa's strikes into neighboring countries, making the prospects for a Cuban withdrawal more difficult.

Van Dunem also said his government still rejects holding direct talks with Jonas Savimbi's National Union for the Total Independence of Angola (UNITA), the insurgency there backed by South Africa and now receiving $15 million in covert military aid from the United States as well. The Reagan administration has been pressing Angola to open talks with UNITA.

Calling UNITA "an extension of the South African army" and the main cause of wide-scale economic destruction in Angola, Van Dunem said, "If we have to negotiate, it's with South Africa we will negotiate."

"How can the Angolan people negotiate with those who are destroying the country?" he added.

Van Dunem denied that his government is preparing "an especially big offensive" against UNITA forces this summer, as Savimbi has predicted, but indicated it will launch its usual dry-season attacks and is expecting "massive" rebel defections this year.

Van Dunem, Angola's economic "czar," said he is concerned about the worsening "polarization" of conflicting interests between his nation and the United States, noting both the Reagan administration's support for Savimbi's forces and several congressional bills calling for the imposition of a trade embargo on Angola.

The minister said the bills, if enacted, threaten to damage "fundamentally" the economic interests of the United States and an increasing number of American firms doing business in Angola, particularly in the oil sector.

The bills would cut off Angolan oil exports to the United States, which now takes about two-thirds of all Angolan exports. Chevron's subsidiary in Angola, Cabinda Gulf, has a $1.3 billion investment there and accounts for the bulk of the oil production that provides all the government's hard currency.