President Reagan intends to veto legislation imposing sanctions on South Africa but may take executive action that would penalize the Pretoria government, administration officials said today.

These officials said Reagan is likely to prohibit the sale of computers to departments of the South African government that administer apartheid and to forbid government loans to companies that refuse to accept equal-opportunity guidelines.

But they said he is determined to veto any bill limiting U.S. investment in South Africa on grounds that this would harm blacks and unfairly penalize a white minority regime he believes is moving away from apartheid.

The president has not announced his intentions, although he has been critical of the sanctions legislation that has passed both chambers of Congress and will be up for final approval when the Senate reconvenes Sept. 9. Reagan's national security affairs adviser, Robert C. McFarlane, has said the president's decision will be guided in part by the political situation in South Africa at the time.

Despite the president's view that South Africa has made progress, White House officials are growing increasingly restive over what they see as the failure of all parties in that country to develop a dialogue that could lead to further reforms.

The administration's difficulties over South Africa have led to conflicts within the White House between officials who advocate increased pressure on the Pretoria government and others who want to hold off such pressures.

White House spokesman Larry Speakes, in an attempt to publicly prod leaders of Pieter W. Botha's government, said today: "It is clear there is a crisis of confidence in South Africa. For a dialogue to start it is essential that the South African government clarify what the dialogue will be about and to take steps which will build confidence so that negotiations can begin."

Speakes' statement, read at this morning's daily White House briefing, appeared to be an effort to balance indirect criticism he made two days earlier of Nobel prize-winning Bishop Desmond Tutu for declining to participate in a meeting between Botha and a group of church leaders.

Today, Speakes referred to Tutu as a "recognized black leader" who had met privately with Reagan. An official said that this was an attempt to leave a "clear inference" that Botha should be willing to sit down with Tutu in a private meeting. But it was stated indirectly, the official said, because of South African sensitivity about policy pressures from outsiders.

Tutu has been scornful of Reagan administration criticism of his conduct, saying he cannot take it seriously.

A White House official said today that the administration had been embarrassed by the Rev. Jerry Falwell's denunciation of Tutu as "a phony" and by what one official called Falwell's "overenthusiastic" support of Pretoria. Falwell, leader of the Moral Majority, has been a prominent supporter of Reagan.

Today, Speakes declined to comment on anything Falwell has said about South Africa or Tutu.

A senior official said that White House communications director Patrick J. Buchanan, an opponent of sanctions against the South African regime, had encouraged Falwell to speak out.

"We're between a rock and a hard place on this one," a senior official said. "What we should be doing is toning down comment of this Falwell's kind, not encouraging it."

Buchanan also met in the White House earlier this week with a group of conservatives in an attempt to muster support for vetoing sanctions legislation, officials said. They said the White House wants conservatives to emphasize that the Botha government is a "reformist" one that has made progress in eliminating some of apartheid's most objectionable features.

This view was expressed last week in the conservative publication Human Events, which is often read by Reagan. Human Events termed the Botha regime "a reformist government that has been systematically eliminating the apartheid system. Sanctions against reformers hardly make any sense."

Buchanan's efforts have brought him into conflict with McFarlane, who has questioned the qualifications of Buchanan and others to deal with intricate foreign policy issues.

McFarlane met early this month with a South African delegation headed by Foreign Minister Roelof F. (Pik) Botha (no relation to President Pieter Botha). McFarlane emerged from that meeting hopeful that the South Africans would announce significant reforms and he has made no secret of his disappointment at the Pretoria government's intransigence.

Today, when Speakes was asked whether the administration's attitude was "one of disappointment at what has transpired thus far," he answered, "Yes." In answer to another question, Speakes said he saw "not much" progress toward negotiations since President Botha's speech last Thursday in which he rejected specific reforms to dismantle apartheid but suggested possible talks about the country's future.

Privately, White House officials believe that Reagan is much more likely to muster support for a veto if he can show evidence of serious negotiations on Botha's part when the sanctions bill reaches his desk in mid-September.