The United States is sending a high-level delegation, including a black senior State Department official, to attend the funeral of black South African leader Steve Biko, who died in prison under mysterious circumstances last week.

The move, which underscores growing America, pressure on South Africa to change its system of racial segregation, is "obviously a speical gesture" to show how the U.S. government feels about Biko's death, a diplomatic source said.

The State Department said the funeral in King William's Town. Biko's home town, would be attended by U.S. Ambassador William Bowdler; Donald F. McHenry, deputy U.S. ambassador to the United Nations: and Donald Petterson, director of the Starte Department's office of Southern African Affairs. McHenry is black.

Since announcing Biko's death Sept. 12. South Africa has come under mounting criticism, especially as conflicting versions have come out over just how Biko became the 21st non-white to die in detention in the last year and a half.

Justice Minister Jimmy Kruger first linked his death to a hunger strike, but then denied that and said determination of the cause would have to wait several weeks for results of an inquest. Since then there have been reports that Biko suffered multiple brain and body injuries before dying.

Other Western nations are also planning to join the U.S. gesture by sending diplomatic representatives - although at a lower level - to the funeral, the Manchester Guardian reported from Johannesburg. The paper said Britain was sending the No. 2 man at the Pretoria embassy and other embassies are following suit.

A Washington source described the gesture by European nations as an important step; since generally they have been less active in South Africa's black community than the Americans.

A spokesman for the South African embassy here said it had not been informed of the U.S. plans to send a delegation to the funeral and had no comment.

The U.S. move is the latest in a series of efforts to increase pressure on South Africa to change its apartheid system.

Vice President Mondale, after a meeting in Vienna with South African Prime Minister John Vorster in May, said there is a "fundamental and profound disagreement" between the two governments over the issue. He added that continuing racial discrimination and denial of political rights to blacks would bring a "worsening of relations" with the United States.

Mondale's statement ended an eight-year period of increased American accommodation of the white minority government by the Nixon and Ford administrations. Former Secretary of State Henry Kissinger had generally followed a policy of trying to curry favor with Sout Africa to gain its help in bringing about an end to the Rhodesian crisis.

Secretary of Stare Cyrus Vance continue the U.S. pressure last week, criticizing the circumstances of Biko's death, calling for an investigation and saying the United States was "shocked and saddened."

About 20,000 mourners are expected to attend Biko's funeral amid tight police security Sunday in Ginsberg Township outside King William's Town, about a thousand miles southeast of Johannesburg. Biko, the leader of the black-consciousness movement, was regarded as a major voice for a moderate solution of South Africa's racial situation.

Criticism of South Africa over Biko's death continued in Washington yesterday when 11 members of Congress called on South African Ambassador Donald Sole to request that the International Red Cross be allowed to investigate the death.

The ambassador rejected the request, saying such an investigation would be "a slur on the South African medical profession" and could create a blacklash within the country, according to a congressional aide who attended the meeting.

The delegation, led by Rep. Don Edwards (D-Calif.) and Thomas Downey (D-N.Y.), said at a press conference following the 90-minute meeting that at no point did Sole express regret over Biko's death.

He "only said that it was handled in an unfortunate manner," said Rep. Andrew Maguire (D-N.J.). This was taken as a reference to the unfavorable international publicity.

Downey and Maguire said they plan to establish a group to monitor the fate of political prisoners in South Africa. They also plan to introduce a resoution next week in the House calling for a Red Cross investigation of Biko's death, they said.

In another development, the State Department said South Africa had arrested and expelled Andrew Silk, 24, a free-lance correspondent for the American magazine. The Nation.

Silk, the son of New York Times business columnist Leonard Silk, was doing research at the University of Cape Town on South African racial policies, his father said.

The elder Silk said his son was put on a plane to London without being allowed to take any possesions, including the research he was doing with the permission of the government.