A nuclear engineer who formerly worked for Westinghouse Electric Corp. pleaded guilty yesterday in federal court to conspiracy and tax evasion.

Initially, Mark M. Kaushansky, 55, of Monroeville, was charged with helping Russia's former atomic energy minister steal more than $9 million in aid money from the U.S. Department of Energy.

But the plea before Senior U.S. District Judge Maurice B. Cohill included just nine of the original 20 counts against him, and they all related to tax evasion.

"He admitted there's some tax problems," said Mr. Kaushansky's defense attorney, Fred Thieman. "It's been our position from the beginning: We denied there was a scheme to skim money from the energy contracts with Russia."

Now the question will be how much money Mr. Kaushansky owes in unpaid taxes.

The government contends the amount is more than $5 million, dating to the mid-1990s. Mr. Thieman, believes, however, that the loss is "substantially lower."

"We intend to show it's neither the magnitude [nor] underlying scheme the government alleged," Mr. Thieman said.

He hopes to convince the judge at Mr. Kaushansky's sentencing hearing in February that the money the government alleges was involved in the case is not taxable in the United States.

At a loss between $2.5 million and $7 million, Mr. Kaushansky would likely face a prison term of 46 to 57 months.

The sentencing hearing, scheduled to begin on Feb. 5, is expected to last at least four days for both sides to dispute that figure.

Mr. Kaushansky came to the United States from Ukraine in 1979. He met his co-defendant, Dr. Yevgeny Adamov, in 1990 when acting as a translator for him in talks with Westinghouse officials.

According to the U.S. attorney's office, Mr. Kaushansky and Dr. Adamov began working together. They incorporated two businesses, one in Pennsylvania and another in Delaware, and used two shell investment companies, with accounts in the United States, France and Monaco, to divert some of the money earmarked for NIKIET, a Russian nuclear research institute headed by Dr. Adamov.

That institute was designed to modernize nuclear reactors in Russia and Eastern Europe like the one at Chernobyl where there was a meltdown in 1986. Sixteen different countries contributed funds to it, including the United States.

As part of his plea agreement, Mr. Kaushansky agreed to forfeit any proceeds in the bank accounts in Monaco. He did not, however, agree to cooperate in the government's case against Dr. Adamov.

The Adamov case has been put on an indefinite hold since Swiss officials ruled in December that Dr. Adamov would be returned to Russia to stand trial instead of being extradited to the United States.