WASHINGTON (AP) _ President Bush told three leading South African foes of apartheid Thursday that he would press ''in every way possible'' to end that nation's system of racial separation, his spokesman said, but gave no indication of any change in U.S. policy.

Nonetheless, the three men with whom Bush met - Archbishop Desmond Tutu, the Rev. Allan Boesak and the Rev. Beyers Naude - said they were impressed that Bush showed an open attitude to their concerns.

Tutu, who heads the Anglican Church in South Africa, was complimentary of Bush's attitude and expressed hopes for progress with his administration.

''I think there is a very warm openness and we think the door stands ajar. No door has been slammed in our face,'' Tutu said after the 20-minute meeting, also attended by presidential Chief of Staff John Sununu and National Security Adviser Brent Scowcroft.

Presidential press secretary Marlin Fitzwater said Wednesday that Bush continues to view additional sanctions against the minority white government of South Africa as ''counterproductive.''

Tutu and his colleagues contrasted Bush's attitude to that of his predecessor, Ronald Reagan.

Once Reagan opposed economic sanctions against South Africa, Boesak said, anti-apartheid activists felt ''there was no further possibility of even discussing the issue.''

Reagan vetoed the sanctions but Congress overrode him. They banned new U.S. investment in South Africa; barred imports of South African coal, steel, uranium and textiles, and prohibited South African airliners from landing in the United States.

Tutu said after meeting with Bush that he had urged the president to ''take the moral leadership'' toward ending apartheid.

''We do not want to be overly optimistic,'' Tutu told reporters. But he said he was impressed that Bush wanted to be ''a catalyst for change'' and ''a positive influence.''

Boesak added, ''The very fact that he values the opinion of those of us who represent black people in South Africa, that in itself is a sign that we did not get in the same measure from the previous administration. ''

Tutu said there were no specific indications of a change away from Reagan administration policies. ''But the way we were received, the fact that we were received'' was a hopeful sign.

The archbishop said the three asked Bush to urge the Pretoria government to negotiate with representatives of the South African black majority.

Boesak spoke to Bush about the need to give hope to young South Africans, ''and that touched a responsive cord,'' Tutu said.

''We said we wanted the United States ... to take the moral leadership of the world in helping to end apartheid and bringing the South African government to the negotiating table,'' the archbishop said.

To that end, Bush and Congress should support new economic and diplomatic sanctions intended to pressure financially strapped South Africa, the group told a news conference.

Boesak said the most effective sanctions would target the South African coal, oil and gold-mining industries.

The three clergymen said they did not specifically discuss sanctions with Bush, but do hope to have further talks with his administration.

Speaking for the administration, Fitzwater said that officials ''will be looking at ways to best use American pressure, influence and leverage to bring about justice and equality to South Africa.''

Fitzwater said that the president ''shares the archbishop's abhorrence of apartheid'' and had ''promised to stress his opposition'' to apartheid ''in every way possible.''

Meeting with reporters a day earlier, Fitzwater said Bush sees further sanctions as ''counterproductive.''

Fitzwater said after Thursday's meeting that Bush had issued an invitation to Albertina Sisulu, one of the leaders of the United Democatic Front in South Africa, to visit the United States.

She is ''restricted'' in her homeland, meaning she cannot speak at public rallies or be quoted in news accounts. State Department officials denied the invitation was an attempt to provoke Pretoria to give her a passport.

The Thursday meeting came as U.S. officials prepared for the visit of F.W. de Klerk, who is expected to succeed P.W. Botha as president of South Africa after Botha resigns in September. De Klerk would be the first top South African leader to officially visit here in 30 years.

Anti-apartheid leaders are looking to De Klerk's ascendancy, along with the new administration in Washington, as a window of opportunity for change. De Klerk has called for political reforms, but opposes complete enfranchisement for blacks, who comprise 85 percent of the nation's population.

1720EDT