The president has chosen to use the occasion of the first anniversary of Congress' enactment of economic sanctions against South Africa to reopen last year's debate. His report argues that sanctions "are not the best way to bring freedom to that country," that they have "put a brake on any inclination toward fundamental reform by the South African government," and that they have had only a "minimal" impact on the South African economy.

This unfortunate approach demonstrates that the White House still does not understand why Congress passed the legislation in the first place. In fact, the President's Report misses the point entirely and does not begin to tell the story of what the sanctions have accomplished.

One of Congress' most important aims in enacting this legislation was to repudiate the administration's policy of constructive engagement and send a strong message of support from the American people to the 27 million nonwhite people living under apartheid. This was accomplished at the very moment Congress overrode the president's veto. As the new U.S. Ambassador to South Africa, Edward Perkins, said soon after he arrived in Pretoria: "As a statement of abhorrence by the American people of a hated system, {the legislation} was an unmitigated success. There is no question about where the American people stand with respect to South Africa and its government at this time."

Although modest in their impact, the sanctions went far beyond anything that any other major Western power had done to register disapproval of apartheid. They have moved the United States into the forefront of the worldwide effort to end apartheid. For the first time in a long time, black South Africans saw the American people as allies -- not enemies -- in their struggle.

Throughout South Africa, the sanctions were warmly welcomed by those they were intended to assist. One week before he was arrested last December, the young South African journalist, Zwalake Sisulu, described the impact of the sanctions legislation: "We really felt heartened when the veto of sanctions was defeated. The voting was telecast live here, and people were sticking to their TV sets watching. For years the face of the American government was only the President of the United States. So we felt relieved." Sisulu remains in detention today, ten months after his arrest, without trial and with no charges pending.

Another aim of the sanctions -- to restore the good standing of the United States in the rest of Africa -- was also achieved. At the time of the vote, Robert Mugabe, the prime minister of Zimbabwe -- not known to be a warm or enthusiastic friend of the United States -- was in New York to address the General Assembly. He held a special press conference to thank the American people. The president of Zambia, Kenneth Kaunda, now the new Chairman of the Organization of African Unity, thanked Congress "for a job well done; the sanctions have assisted us greatly." He praised the sanctions as "the most important and eloquent statement of moral condemnation in a decade."

A third objective was to begin a process of cooperation with other countries. No one in Congress expected U.S. sanctions to end apartheid in South Africa, certainly not in one year. And no one thought that such modest measures would have a major economic impact. But we did expect the sanctions to become part of a coordinated international effort aimed at producing the kind of external economic pressure that would make a difference in South Africa. That was why, in the legislation, Congress explicitly called on the administration to pursue such cooperation.

It is therefore surprising to discover that the President's Report fails to mention the administration's decision, on Feb. 20 of this year, to veto the U.N. resolution that would have launched such an effort. That action was inconsistent with both the letter and the spirit of the legislation and destroyed the possibility of concerted international action. And that veto is why the President's Report is able to say that the economic impact of the U.S. sanctions has been "minimal."

In his report, the president points out that, in the recent all-white elections in South Africa, the governing party's strength increased and the pro-apartheid Conservative Party replaced the anti-apartheid Progressive Federal Party as the official opposition. But there is much more going on in South Africa than the politics of the white supremacists.

It is true that the sanctions were sharply criticized by most segments of the South African white community, but even there, they had a positive impact. As a statement of rejection and repugnance by the leading nation in the Western World, the sanctions were unprecedented. Their significance was debated and discussed in the ruling circles of Afrikanerdom. During this past year, the bulwark of Afrikaner spiritual life and culture, the Dutch Reformed Church, turned against apartheid. The Broederbond, the secret society of the Afrikaner power elite, began talking openly about power-sharing. And 300 faculty leaders at Stellenbosch University, the citadel of the Afrikaner intellectual establishment, bolted from the National Party in the past election.

While these developments may not have been a direct result of the sanctions, President Reagan's overwhelming defeat at the hands of Congress certainly contributed to the Afrikaners' growing sense of vulnerability and isolation and may have hastened the breakup of the monolithic Afrikaner community.

The United States cannot end apartheid; that is a task and challenge for South Africans. But we should not make it more difficult for the forces of freedom to prevail in that country. We should do nothing that can be construed as providing aid or comfort to the apartheid regime. And we should do more to strengthen the sanctions in place.

Increased repression inside South Africa over the past year is ample evidence that Congress did the right thing in distancing the United States from that regime. Instead of using the first anniversary of that historic legislation to renew his opposition to the sanctions, President Reagan should be making a greater effort to persuade our friends and allies to join us in new initiatives against apartheid. To unify the industrialized nations of the world in a common anti-apartheid policy is the next step. It may be unrealistic to hope that the president will take that step, but it would be sad if America's role as the natural leader of the world anti-apartheid effort had to await the election of a new president.

The writer is a Democratic senator from Massachusetts.