JOHANNESBURG, JUNE 17 -- The Bush administration is asking Congress to approve an additional $10 million to $15 million in covert military aid to the Angolan rebel movement led by Jonas Savimbi even as it is engaged in "extensive discussions" with the Soviets on ways to end Angola's 15-year-old civil war, according to administration and other sources.

The supplement to the $50 million already budgeted this fiscal year for the Central Intelligence Agency aid program to Savimbi's National Union for the Total Independence of Angola (UNITA) would come in the form of reprogrammed funds that require the approval of the Senate and House intelligence committees.

According to one source, the request was formally approved by the committees earlier last week, but this information could not be immediately confirmed. The request for additional aid follows Savimbi's claim early last month of a major victory in forcing the Angolan government to call off an offensive aimed at penetrating deep into UNITA territory in southeastern Angola.

It also comes as black American leaders -- including Jesse Jackson and Randall Robinson, the director of TransAfrica, a leading lobby on African matters -- have begun a campaign to force an open congressional debate on the covert U.S. aid program to UNITA. The black leaders met June 12 with House Speaker Thomas Foley (D-Wash.) to press their demands for such a discussion.

Robinson afterward expressed dissatisfaction with Foley's response and accused Democratic Party leaders of a "failure of character and leadership" in not opposing the administration's UNITA aid program more forcefully.

The additional U.S. aid request follows statements by Savimbi that U.S. military assistance rushed to his forces by the CIA starting in January was crucial in turning back the Angolan offensive. According to reports in the South African press, U.S.-provided Land Rovers and Toyota Land Cruisers armed with 106-mm recoilless rifles made the difference in countering Soviet-supplied fast-moving armored personnel carriers and medium tanks used by the Angolan army.

The Bush administration has been holding "extensive discussions" with the Soviet Union on ways to end the Angolan conflict, according to testimony given Wednesday by Secretary of State James A. Baker III before the House Foreign Affairs Committee.

Baker refused to comment on a report that the Soviet Union has proposed a substantial cut in its military aid to the Angolan government if the United States ends its covert assistance program to UNITA.

But Baker later told the Senate Foreign Relations Committee that any mutual cuts in U.S. and Soviet military aid to the two warring Angolan parties would be part of an overall agreement including a cease-fire "and a commitment that there could, in fact, be open, free and fair elections."

Soviet military aid to Angola last year has been estimated by the United States at $800 million, down 40 percent from the $1.2 billion provided in 1988. U.S. aid to UNITA last year was between $30 million and $40 million.

The Bush administration has proposed to the Soviets that the two governments sponsor peace talks between the Angolan government and UNITA in Geneva. But the Angolan government has decided it prefers to use Portugal as a go-between.