The Supreme Court yesterday ordered Feodor Fedorenko, once an armed guard at the Nazi concentration camp at Treblinka, stripped of his citizenship because he concealed his past when he entered the country in 1949.

It was a hard-fought legal and symbolic victory for the government, which saw the case as a demonstration 35 years after the Holocaust of its continued determination to rid the country of death camp officials, however low they were in the hierachy. Roughly 240 alleged Nazis are still being investigated for deportation by the Justice Department.

The 7-to-2 ruling, which government lawyers said might be applied later to Cuban refugees who lie about their backgrounds, gave the government all it asked for and possibly more: an immigrant's failure to disclose a material fact on a visa application is sufficient grounds for revocation of citizenship and deportation, the court ruled.

It is not necessary to show that the immigrant committed any atrocities or that he acted voluntarily. The mere failure to disclose a fact that would have made him ineligible for entry can result in later loss of citizenship and deportation, Justice Thurgood Marshall wrote for the majority.

The fact that Fedorenko has a "record of good conduct over the past 29 years" and that there are "reasonable doubts" the he committed crimes at treblinka does not give the court discretion to let him stay here. That, the court said, "would excuse illegal or fradulent procurement of citizenship."

The government will now begin deportation proceedings against Fedorenko, a 74-year-old retired factory worker who was living quietly in Connecticut before his discovery by federal immigration authorities. Fedorenko's only relatives live in the Soviet Union, his lawyer said yesterday, and he has no idea where he might go.

About 800,000 people were murdered at Treblinka in Poland. The government produced witnesses 30 years later who identified Fedorenko as the guard who shot Jewish prisoners after making them crawl naked on all fours, who chased women into gas chambers, beating them as he went, and who carried a steel-tipped whip, used a flay prisoners upon their arrival at the camp.

A federal judge found the evidence insufficient, however, and Fedorenko remains innocent of those crimes. He did admit, however, the had fired in the direction of escaping prisoners during a 1943 Treblinka uprising. But he said he, too, was a prisoner at the camp, having been captured by the Nazis while serving in the Soviet Army. His work as a guard was involuntary, he argued.

After the war, U.S. law specifically made war criminals and others who participated in persecution ineligible for entry into the country. When Fedorenko entered in 1949, he said he had been a farmer and factory worker during the war years and made no mention on his visa application of his Treblinka experience.

In 1970, he applied for and received naturalization as a U.S. citizen. Immigration authorities called him for questioning later during an unrelated investigation of possible entry of former Soviet citizens who participated in a Ukrainian underground organization that collaborated with the Nazis.

During that questioning, he blurted out the fact that he had been a guard at Treblinka. The government then moved to revoke his citizenship and deport him because of his earlier failure to state that fact on the visa application.

"The plain language of the law," Marshall wrote yesterday, left no room for doubt that if Fedorenko "had disclosed the fact that he had been an armed guard at Treblinka, he would have been found ineligible for a visa. . . ."

Neither the fact that the government could not provide clear and convincing evidence of Fedorenko's specific crimes nor Fedorenko's claim of involuntariness is relevant, Marshall said. The Displaced Persons Act, under which refugees were admitted or denied admission after World War II, made no distinction between voluntary and involuntary. It made "all those who assisted in the persecution of civilians ineligible for visas," the court said.

Justices Byron White and John Paul Stevens dissented. White said the court should have dwelled not so much on Fedorenko's visa application but on what he said when he applied for citizenship in 1970. Stevens said that the court's unwillingness to consider the involuntariness argument means that a Jew, who was forced to help in the death camps, could conceivably be deported.

In other decisions yesterday:

The court upheld, 7 to 2, Minnesota's right to ban the sale of milk in plastic containers. That state's law had been challenged (Minnesota vs. Clover Leaf Creamery) on the grounds that it discriminated against plastic manufacturers. The court said the Minnesota legislature had a rational basis -- prevention of pollution -- for its law and that was all that was necessary.

The court ruled unanimously that police may stop vehicles when "the totality of circumstances" suggests its occupants may be involved in a crime. The decision in U.S. vs. Cortez stemmed from a police stop of a camper in Arizona and resulting charges of transporting illegal aliens against its occupants.