Some federal employees have purchased bogus academic degrees at taxpayers' expense to stroke their egos and help them qualify for jobs and promotions, congressional investigators said yesterday.

Federal officials acknowledge, however, that they do not know how many workers are involved, how much money has been misspent or how to guarantee an end to it.

An eight-month General Accounting Office investigation found that more than a dozen federal agencies had paid more than $169,000 to two unaccredited schools suspected of being diploma mills -- California Coast University in Santa Ana and Kennedy-Western University in Agoura Hills, Calif. Those schools and Pacific Western University in Los Angeles, another unaccredited institution, identified 463 federal employees from more than 25 agencies among their students, including 257 students from the Department of Defense.

The investigation also found that 28 senior-level employees in eight agencies have degrees from diploma mills or other unaccredited schools. The report did not reveal their names. Diploma mills operate without state or professional oversight, and require little or no serious coursework.

Robert J. Cramer, the GAO official who directed the effort, said the investigation was hampered by the fact that federal agencies do not organize data in a way that payments to diploma mills can be identified. He said the GAO had referred some of its findings to inspectors general in various agencies.

"We know for a certainty that what we have is only part of the picture," Cramer said yesterday during a hearing of the Senate Governmental Affairs Committee. "It's a much larger problem than the evidence we have to date shows."

Committee Chairman Susan Collins (R-Maine) agreed: "I believe this is just the tip of the iceberg."

Federal law allows agencies to reimburse employees for degrees obtained from accredited institutions, but a loophole permits payment for individual courses offered by unaccredited schools, he said.

Lewis M. Phelps, a spokesman for Kennedy-Western University, said the online school was unfairly tarnished in the report.

"The basic equation GAO seems to have come up with is 'no accreditation, no good,' " Phelps said. "We don't think that's valid."

The buying of bogus degrees by federal employees is an abuse of tax dollars if the government picks up the cost, GAO officials and lawmakers said. It also undermines the integrity of hiring and promotions, and could help unqualified or unethical people land jobs affecting national security.

The GAO said bogus-degree recipients include three managers with emergency operations responsibilities and security clearances at the National Nuclear Security Administration, an agency within the Department of Energy.

One of those managers told investigators that in 1996 he paid $5,000 for a master's degree from LaSalle University, an unaccredited school in Louisiana, to advance his Air Force career. The degree, which the employee branded a "joke," required no tests or class attendance, and was based on life experience and courses he had previously taken in the military.

Other high-level employees with bogus degrees worked for the departments of Education, Health and Human Services, Homeland Security, Transportation and Veterans Affairs, and the Small Business Administration. A bogus degree held by a human resources official at the Office of Personnel Management was not funded by tax dollars, and the worker has since left the agency, an OPM spokesman said.

Laura Callahan, deputy chief information officer at Homeland Security, resigned in March amid a flap over a doctorate she received from a diploma mill in a former motel in Evanston, Wyo.

Charles S. Abell, a deputy undersecretary of defense, lists on his department biography a master's degree from Columbus University, a Louisiana institution that appears on a list of diploma mills monitored by Oregon. In a statement yesterday, the Pentagon said Abell "has always been forthcoming about his credentials and has clearly demonstrated his commitment and ability to serve in federal government."

Rep. Thomas M. Davis III (R-Va.), who requested the GAO study with Collins, noted yesterday that OPM has taken steps to combat the problem. They include intensifying educational background checks, increasing training for managers and clarifying government forms to help root out phony degrees.

Davis said the federal government should develop lists of diploma mills and of approved institutions. He said, however, that with the rise of online learning and legitimate but unaccredited schools, "it's not real easy at this point to define what is bogus and what isn't."

"We need to put more investigators into this, because this is a massive fraud on taxpayers," Davis said. ". . . I don't think we want to go on a witch hunt at this point for people, but we want to give them a chance to come clean. And if they have bogus degrees, I think they need to come forward."