WASHINGTON (AP) _ The Tennessee Valley Authority won a multi-billion dollar government contract to produce tritium, a form of hydrogen that boosts the power of nuclear warheads, lawmakers announced today. d The Energy Department has selected the TVA's Watts Bar Nuclear Plant near Knoxville for its tritium production. TVA's Sequoyah nuclear plant outside Chattanooga, Tenn., will serve as a backup source, confirmed Republican Sens. Strom Thurmond of South Carolina and Jeff Sessions of Alabama.

Tritium has not been produced in the United States since 1988, when the government shut down its last weapons reactor at the Savannah River Site in Aiken, S.C.

Energy Secretary Bill Richardson was expected to formally announce the decision late today. TVA spokesman Gil Francis said the agency would have no comment until Richardson made his official announcement.

Among other options that had been considered by the Energy Department was the TVA's unfinished Bellefonte nuclear plant outside Scottsboro, Ala. It also weighed the ideas of building a new linear accelerator at the Savannah River Site and using the Fast Flux Test Facility, a nuclear reservation in Hanford, Wash.

TVA officials had pushed the Bellefonte option, hoping to obtain federal financial help to complete construction of the plant. But the Energy Department asked TVA earlier this fall to submit a detailed plan for the Watts Barr-Sequoyah option, considered the least expensive of the three proposals.

The House approved legislation earlier this year that would have blocked the use of a commercial nuclear reactor to product tritium, but the measure failed in the Senate. Supporters of the House-passed measure argued that using a commercial reactor would breach the long-standing separation of commercial and defense uses of nuclear power.