SAN FRANCISCO - The nation's top lab for nuclear-weapons design has laid off hundreds of workers, raising concerns about a brain drain and stirring fears that some of these highly specialized scientists will sell their expertise to foreign governments, perhaps hostile ones.

Because of budget cuts and higher costs, Lawrence Livermore National Laboratory laid off 440 employees May 22 and 23. In the last 21/2 years, attrition and layoffs have reduced the workforce of 8,000 by about 1,800.

According to a list obtained by the Associated Press, about 60 of the recently laid-off workers were engineers, about 30 were physicists, and about 15 were chemists. Some, but not all, were involved in nuclear-weapons work or nonproliferation efforts, and all had put in at least 20 years at the lab.

Some lawmakers and others say they fear the loss of important institutional knowledge about designing warheads and detecting whether other countries are going nuclear.

Also, Sen. Dianne Feinstein (D., Calif.) said the layoffs at Lawrence Livermore and two other big U.S. weapons labs represent "a national-security danger point." These unemployed experts might take their skills overseas, Feinstein said.

The possibility is also on the mind of the nation's top nuclear-weapons official, National Nuclear Security Administration chief Tom D'Agostino. "Always in a situation where people leave under less-than-ideal circumstances, we worry about that," he said, "and it's something I assure you we're looking at closely."

NNSA spokesman Bryan Wilkes said the agency regards the possibility of a hostile government picking up laid-off workers as "highly unlikely," in part because these are American citizens who have responsibly held high-level clearances for many years, and because federal law provides stiff penalties for divulging nuclear secrets.

With a self-imposed nuclear test ban in place since 1992, maintenance of the warhead stockpile, Lawrence Livermore's top responsibility, is performed on supercomputers. So is the task of designing a new generation of warhead, which the lab won the right to do last year.

The layoffs have reduced the lab's roster of experts with experience gleaned from taking part in actual nuclear tests. "Designing, building and seeing a device go off is very different from designing a device and handing it to a computer jockey," said physicist Ken Sale, who was laid off.

Democratic Rep. Jerry McNerney, whose district includes part of the lab, said the stakes were especially high as the United States tries to divine through science what other countries are doing inside their weapons programs.