A blue-ribbon scientific panel, appointed by Congress to review the U.S. nuclear stockpile, has recommended that the Department of Energy design a new, billion-dollar plutonium weapons plant and organize teams at the nation's nuclear laboratories to design new warheads for the first time in more than a decade.

The panel, chaired by John S. Foster, former head of Lawrence Livermore National Laboratory and a senior Defense Department official from 1965 to 1973, said "a paramount concern" is the uncertain future reliability of the already 20-year-old plutonium "pits" at the heart of America's nuclear warheads, according to a declassified version of its report obtained by The Washington Post.

The report urges the Energy Department to start immediately on the "conceptual design" for a plant to replace the former plutonium facility at Rocky Flats, Colo., which closed in 1989. The panel warned that it could take up to 15 years to put such a plant into operation, mainly because of "political and environmental issues" rather than technical ones.

The findings of the panel, which included former defense secretary James R. Schlesinger and Harold M. Agnew, former head of Los Alamos National Laboratory, are likely to be welcomed by members of Congress who fear a decline in the U.S. nuclear deterrent and recently voted to reject the Comprehensive Test Ban Treaty.

The Foster panel's recommendations for more spending on the U.S. nuclear program are echoed in proposals, to be released today, from an internal review of the Energy Department's "stockpile stewardship" program, which seeks to ensure the reliability of American warheads. The review concluded that costs will rise because some of the reductions in nuclear weapons expected from U.S.-Soviet arms control treaties have not materialized.

It noted, for example, that the Energy Department has not been planning to refurbish older warheads for the Minuteman III land-based intercontinental ballistic missile because those weapons were to be retired with the ratification of the START II.

But the Russian parliament still has not ratified START II, and the Russian government has warned that the U.S. rejection of the Comprehensive Test Ban Treaty, along with America's efforts to amend the landmark 1972 Anti-Ballistic Missile treaty, could spark a new arms race.

In sum, "arms control issues may force Energy to keep [old warheads] in the stockpile," the review said.