The General Accounting Office yesterday released an interim report concluding it could cost more than $8.8 billion to complete and operate the controversial Clinch River fast breeder reactor for five years.

The GAO figure, which is more than double the Department of Energy's estimate of $3.6 billion, does not include a variety of items that congressional critics of the advanced nuclear reactor estimated could push the government's final cost to over $10 billion.

"Weapons' overruns pale in the face of Clinch River," said Rep. John D. Dingell (D-Mich.), chairman of the House Energy Committee, who requested the GAO study.

The major factor cited by the GAO in arriving at the higher figure was that the Energy Department's estimates for Clinch River do not include imputed interest, the cost of the interest the government pays on money borrowed to finance federal projects.

The GAO estimated that cumulative imputed interest on the Clinch River breeder through 1994, the end of the project's five-year demonstration, might exceed $3.9 billion.

While the GAO recognized that imputed interest is "not normally associated with cost estimates" of programs that come before Congress, it noted that the Energy Department includes imputed interest as part of the cost of operating its uranium enrichment facilities, which the government also funds.

But Deputy Assistant Energy Secretary Gordon L. Chipman said imputed interest is figured into the cost of funding the enrichment facilities "because they are required by law to recover all their costs -- including interest -- from their customers.

"The difference is that Clinch River is a research and development project," Chipman said.

"It is simply unfair to add imputed interest to the cost of Clinch River when it is not part of the price of any other research and development project being considered by Congress."