The Reagan administration has failed to carrry out certain provisions of antiapartheid legislation passed by Congress last year against South Africa and ignored or dragged its feet on others, according to a congressional report.

The report by the General Accounting Office (GAO), an investigative arm of Congress, also details how South African exports of strategic materials have slipped through a loophole in the 1986 Comprehensive Anti-Apartheid Act. They reached the United States through Japanese, Spanish, West German and Taiwanese intermediaries to the detriment of the troubled U.S. uranium conversion industry, it said.

Sen. Edward M. Kennedy (D-Mass.) released the report this week during Senate hearings on U.S. policy toward South Africa. Senate and House committees are considering eliminating loopholes in the act and strengthening sanctions.

The act stated the "sense of Congress" that the United States should seek U.N. Security Council measures against South Africa similar to U.S. sanctions. But the administration voted against additional mandatory sanctions in the Security Council, the report said.

President Reagan's has asserted in a letter to the Senate Foreign Relations Committee that he has fulfilled his obligations under the act "fully and faithfully."

But the report says "no effort was made" by the administration to convene a conference of industrial nations to consider further sanctions, as the act requires.

"Instead, the State Department emphasizes its continuing diplomatic discussions with other nations on possible multilateral steps to bring about an end to apartheid," it said.

The study shows that various government departments have been consistently late with required reports on U.S. dependence on South African exports and its internal politics. A Justice Department report on violations of the Foreign Agents Registration Act by government and opposition groups in subsaharan Africa was more than five months late, the report said.

The GAO report details how banned South African uranium ore and oxide reaches the United States in the form of a gas processed in Europe.

"According to an Energy Department official, the banning of uranium ore and oxide, without specifically banning {the gas}, uranium hexafluoride, hurt the U.S. uranium conversion industry without reducing the amount of South African uranium entering the United States," the report states.

One official estimated that this year uranium hexafluoride of South African or Namibian origin will total about 28 percent of the uranium enriched in the United States and converted into fuel rods for shipment to foreign utilities. Namibia is administered by South Africa's minority white regime.

Details of the uranium ban are currently the subject of a court action against the Nuclear Regulatory Commission.

The Commerce Department, however, has devoted "significant resources" to checking that computers shipped to South Africa are not used for apartheid-enforcing agencies or the police and military, the report said. It found that of all such checks by Commerce this year, 27 percent were carried out in South Africa and that two export license requests were recommended for rejection.