South African Foreign Minister Roelof (Pik) Botha will visit Washington May 14 for discussions with Secretary of State Alexandria M. Haig Jr., State Department officials said yesterday. The officials said the two will discuss the Reagan administration's general policies toward southern Africa and specific proposals concerning eventual independence for the South African-controlled territory of Nambia.

Botha and Haig also are expected to discuss the Reagan administration's controversial request to Congres to repeal a 1976 law known as the Clark amendment after its sponsor, former senator Dick Clark (D-Iowa). It prohibits any U.S. military aid or covert help to rebels fighting the Marxist central goverment in Angola.

The South Africans, and a sizable number of U.S. senators, would like to see that law repealed so that the United States could help, if it wished, the anti-communist forces of Jonas Savimbi's UNITA movement, which continues to fight against the Cuban-backed government in Angola, which borders Namibia.

Haig has said that the law should be repealed on principle because it is a "disabling legislative restriction" inhibiting the president's right to make foreign policy. Haig also said the request to repeal the law did not mean that the administration wanted to intervene in some way in Angola.

The administrationhs request, however, lost its first test on Capitol Hill yesterday when the Africa subcommittee of the House Foreign Affairs Commitee voted, 7-to-0, to reject the proposal. The panel's two Republicans voted with the five Democrats.

The proposal, however, is far from dead. It next goes to the full committee, then to the floor of the House and probably will wind up in a conference committee with the Republican-controlled Senate, where sentiment to repeal is stronger.

Last summer, the Senate approved a similar Carter administration request by voice vote, but the measure was dropped in conference.

The trip by the foreign minister will be his first here since a visit in March 1979 with former secretary of state Cyrus R. Vance. Since taking office, President Reagan has made several statements that have been interpreted here, in Pretoria and in black African states to mean that his administration takes a more friendly attitude toward South Africa than did the Carter administration.

In particular, the South Africans seem more favorably disposed to a proposal Reagan revealed during an interview in The Washington Post earlier this month. That proposal would alter a Western-designed U.N. plan for Namibian independence by requiring that a constitution be drawn up before elections are held.

State Department officials say they believe this will ease South African concerns about preserving the rights of political parties in Namibia opposed to the dominant left-wing guerrilla group known as the South West Africa Peoples' Organization.

The U.N. plan would involve elections to a constituent assembly that would draw up a constitution in what officials here say would be a winner-take-all situation for SWAPO.

Botha's visit here will come after Wednesday's election in South Africa, which officials believe will lead to a more relaxed conversation with the U.S. government. The government of Prime Minister Pieter W. Botha, who is not related to the foreign minister, is expected to win.

The visit also follows harsh words by the prime minister earlier this month after a visist to Africa by assistant secretary of state-designate Chester Crocker.

Botha seemed to think that some of Crocker's remarks did not reflect sufficient conviction that SWAPO was a communist-controlled, Soviet surrogate with the lone goal of "subordinating South-West Africa (Namibia) by brutal force," as Botha put it.

Actually, Crocker said: "There is no question that SWAPO is supported by the Soviets ad their friends at present, but I think it would be an over-simplification to think that that, by itself, accounts for what SWAPO does or would not do if it were to win an election."