Thirty-three House members sent President Reagan a letter yesterday urging him to impose additional economic sanctions on South Africa in light of "the abominable and deteriorating situation" there.

Reacting to reports that the president will not propose other punitive measures as required by last year's antiapartheid legislation, the 17 Republican and 16 Democratic House members asked Reagan to "implement the law" and avoid the impression the United States applies one standard of human rights to the Soviet Union and another to South Africa.

The Comprehensive Antiapartheid Act, signed a year ago today, requires the president to impose further sanctions if he determines that the South African government has made no "significant progress" in one year toward ending its apartheid system of racial segregation and establishing a nonracial democracy.

The White House is expected to release a report today or early next week basically agreeing that little progress has been made, but refusing to impose further sanctions.

Assistant Secretary of State Chester A. Crocker, in a speech prepared for delivery last night at a conference on South Africa in White Plains, N.Y., said U.S. sanctions imposed last year -- including a ban on new U.S. investments in South Africa -- had failed to move the government there. "None of the actions on the part of the South African government that the legislation hoped to achieve has so far taken place," he said.

"The {South African} government's response to external pressure over the past year gives no grounds for hope that more sanctions will produce better results," he said.

The letter, sponsored by Rep. Howard Wolpe (D-Mich.), chairman of the Africa subcommittee, and Rep. William H. Gray III, chairman of the Budget Committee, pointed to the detention of 30,000 people without charge, the deaths of 1,096 and the imposition of draconian press restrictions as evidence of the worsening political situation inside South Africa over the past year.

The letter argues that current U.S. sanctions are "relatively weak and contain several loopholes" affecting only one-third of U.S. imports from South Africa and "virtually no exports," nor had the administration implemented some of the provisions required by the law, the congressmen charged.

The signers said they hoped to avoid "the kind of bitter and divisive conflict" with the White House that occurred last year when Congress overrode Reagan's veto of the anti-apartheid act. There was no indication in the letter, however, what the congressmen propose to do if Reagan refuses to impose further sanctions.