An estimated 24 pounds of plutonium, enough to make two small nuclear weapons, is missing from the Department of Energy's nuclear fuels reprocessing plant at Savannah River, S.C., according to a draft report by the General Accounting Office.

DOE apparently is unable to account for the 24 pounds, which it lists as Material Unaccounted For from 1976 to 1978. It has told GAO that it does not believe any of the plutonium was stolen or sold on the international black market.

One source said the missing plutonium is almost surely stuck to the walls of pipes that carry dissolved plutonium and spent uranium fuel from tank to tank at Savannah River. Reprocessing plants are so intricate that plutonium often passes through 50 miles of piping before it is purified.

The 24 pounds is in addition to 303 pounds of plutonium reported missing in 1977 by the Savannah River plant in the period from 1955 to 1976.

At the time, a spokesman for the Energy Research and Development Administration, DOE's predecessor blamed the missing plutonium on the plant's plumbing.

"It's inevitable," the spokesman said, "that small quantities of the material will adhere to the walls of the pipes as it passes through. Just a coating of less than one hundred-thousandth of an inch on the interior walls of the pipes would account for the entire plutonium difference at Savannah River."