The Reagan administration's plan to repeal the prohibition against overt or covert U.S. aid to rebel forces in Angola ran into strong opposition yesterday from an unlikely alliance that encompassed both liberal Democratic House members and a spokesman for a major oil company.

In the second day of hearings on the proposed repeal of the Clark amendment, Rep. Howard E. Wolpe (D-Mass.), chairman of a House subcommittee on Africa, said that such a repeal would seriously damage U.S. interests throughout black Africa and "play directly into the hands" of the Soviet Union and Cuba, supporters of the Marxist government of Angola.

Wolpe was joined in this criticism by other House Democrats, by former senator Dick Clark (D-Iowa), the author of the amendment, and by Melvin J. Hill, president of Gulf Oil Exploration and Production Co., a subsidiary of Gulf Oil.

Hill said the amendment should be repealed eventually, but that to do so now "would have an extremely negative effect, both in Angola and elsewhere in Africa."

He said this was his "personal view," but it also clearly reflected the attitude of his company and others that have major investments in Angola and have found the government of the west African country to be, in Hill's words, "buusinesslike and nonideological" despite its Marxist philosophy.

The testimony of Hill and others, along with the comments of committee members, including Republicans who showed no great enthusiasm for repealing the amendment, indicated the administration may have serious trouble achieving one of its first objectives on Africa policy.

Angola represents a delicate challenge to the administration, which is still evolving an overall African policy but which has vowed to counter Soviet and Cuban expansionism, in Africa and elsewhere. Angola now hosts an estimated 18,000 Cuban troops, who are helping protect the government against rebel forces led by anti-Marxist Jonas Savimbi.

In an interview last May, President Reagan, then campaigning for the presidency, showed no hesitancy about arming Savimbi -- a policy then and now prohibited by the Clark amendment. "Well, frankly, I would provide them [Savimbi's forces] with weapons," Reagan said.

However, in an interview last weekend with The Washington Post, the president took another approach. He said the Angolan government should first "get rid of the outside forces," the Cuban troops, suggesting that then the United States would try to help bring about a peaceful settlement between the rival factions in the country.

Angola contends the Cuban troops are necessary to protect it from raids by the white-ruled government of South Africa, which has provided aid to Savimbi.

The administration's effort to repeal the Clark amendment is among a number of developments that have alarmed black African nations, which fear they signal the beginning of a "tilt" by this administration away from the policies of the Carter administration and toward South Africa.

Clark told the subcommittee he favors eventual repeal of the prohibition, but only after Namibia, which borders Angola on the south, has gained independence (it is now a South African protectorate), and after the United States has granted diplomatic recognition to the government of Angola.

Clark and other witnesses also warned that no settlement in negotiations on Namibia's independence is possible without Angolan cooperation, and that Angola's willingness to cooperate with Western powers that are involved with the Namibian negotiations would end if the amendment is repealed.

Savimbi is scheduled to visit Washington soon to press his case for support. State Department officials yesterday confirmed that Savimbi met recently in Morocco with an American official later identified by sources as Lannon Walker, acting assistant secretary of state for African affairs.