The Marxist government of Angola, with which the United States has refused to establish diplomatic relations, has sent its highest-level delegation here to seek a change in administration policy and an end to covert U.S. military aid for its rebel opposition.

Led by Pedro de Castro Van Dunem, the No. 2 figure in the Angolan government, the five-member delegation met yesterday with Assistant Secretary of State Chester A. Crocker to discuss the withdrawal of 37,000 Cuban troops, which the Reagan administration has insisted upon before establishing diplomatic ties.

Both Angolan and U.S. officials said Van Dunem was here "on a private visit" and that the meeting did not mark a formal resumption of negotiations over the Cuban troop withdrawal.

The Angolans broke off those talks last March after the administration began providing sophisticated Stinger antiaircraft missiles and other arms to Jonas Savimbi's antigovernment forces.

The negotiations are scheduled to be formally resumed later this month in Luanda, the capital of the former Portuguese colony.

At a luncheon news conference, Van Dunem said his southwest African nation is "completely open" to discussions with the administration, adding, "We want {diplomatic} relations."

The minister, a Politburo member in charge of economic policies, said he had lined up meetings with 20 lawmakers during his six-day stay here and that he has "a big interest" in meeting with as many officials as possible.

But he said he did not expect to meet with Senate Minority Leader Robert J. Dole (R-Kan.), who has introduced a bill calling for a trade embargo against Angola.

Before the delegation arrived here, U.S. officials said they wanted to know whether the Angolans had any new proposals on the Cuban troop issue, saying "the ball is in their court."

The Americans said they would stress the need for additional Angolan concessions on the troop issue at the Luanda meeting in order to overcome the current impasse in the talks.

Van Dunem gave no indication that he has brought any new proposals.

Angola, he said, is adhering to its 1984 proposals to order the withdraw of the Cuban troops after neighboring South African-administered Namibia becomes independent and South African attacks against Angola cease.

"We would like to know what are the proposals of the Americans," Van Dunem said.

However, Venancio de Silva Moura, vice minister of the foreign ministry, said later Angola is prepared to be "more flexible" on "the numbers and timing" for the proposed Cuban withdrawal "depending on the circumstances." He did not elaborate.

Van Dunem disclosed that Angola recently decided to annul its contract with Southern Air Transport, the former Central Intelligence Agency airline involved in sending U.S. arms to Iran and the Nicaraguan contras.

SAT has had a contract for several years with the Angolan state diamond company to provide transportation between Luanda and the interior.

The minister said the government is investigating the line's operations in Angola to see whether it had been involved in espionage activities.