The Supreme Court ruled unanimously yesterday that federal law prohibiting fraud in the sale of securities also applies to the use of stocks as collateral for bank loans.

The pledge of stock to a bank as collateral for a loan is an "offer or sale" of a security and thus falls under the Securities Act, the justices concluded.

The decision stemmed from the conviction of William Rubin, a New York accountant, of conspiracy to defraud Bankers Trust Co. of New York.

Rubin was an officer of Tri-State Energy Co., "a corporation holding itself out as involved in energy exploration and production," said the high court opinion by Chief Justice Warren E. Burger.

Tri-State borrowed $475,000 from Bankers Trust, pledging as collateral thousands of shares of borrowed, or worthless, stock, the opinion related.

Federal law makes it a crime to use fraud "in the offer or sale of any securities."

Rubin appealed his conviction, arguing that he had not tried to sell the securities, but only posted them as collateral for loans and thus had not violated the fraud conspiracy law.

The Supreme Court, however, pointed out that the law defines "sale" to include "disposition of a security or interst in a security for value."

And it said that was clearly what Rubin did: He gave Bankers Trust a potential claim on the securities in exchange for the valuable loans.

In fact, when Rubin's company failed to repay the loans on demand -- after FBI inquiries made the bank suspicious -- Bankers Trust did claim the securities and found it could not recover the value claimed for them.

Of the $475,000 it lent Tri-State Energy, the bank got back only $2,500, the Supreme Court noted.

Chief Justice Warren Burger, writing for the court, concluded, "The economic considerations and realities persent when a lender parts with value and accepts securities as collateral security for a loan are similar in important respect to the risk an investor undertakes when purchasing shares.

"Both are relying on the value of the securities themselves and both must be able to depend on the representations made by the transferor of the securities."

Justice Harry Blackmum filed a concurring opinion in the case.