The son-in-law of Russian President Boris Yeltsin maintained at least two accounts -- which sources said contained more than $2 million -- at an offshore branch of the Bank of New York, a disclosure that could push an expanding U.S. probe of alleged money laundering into the inner circle of Russia's leaders.

Leonid Dyachenko, the husband of Yeltsin's daughter, Tatyana, was a beneficial owner of the accounts at the Bank of New York Trust Co. in Grand Cayman, Cayman Islands, the chairman of the bank, Thomas A. Renyi, told the House Banking Committee yesterday. Tatyana is also an important Kremlin adviser to her father.

Thus far, it is unclear whether the Cayman Islands accounts are linked to nine or more other Bank of New York accounts used to move at least $7.5 billion out of Russia in the past three years. Renyi confirmed the existence of the Dyachenko accounts in response to questions during testimony on the bank's handling of the other investigation [Story, Page E3].

The Cayman Islands accounts may be the first sign that alleged Kremlin corruption reached into the U.S. banking system. Although Dyachenko, an oil trader, could have legitimate business reasons for maintaining the offshore accounts, one U.S. official familiar with the probe called the politically sensitive revelation "an embarrassment" for Russian leaders. He added that law enforcement officials believe the names of other Russian officials will surface in connection with the investigation.

"This is going to lead in all kinds of directions. . . . This isn't the end of the embarrassing kompromat likely to emerge in this case," the official said, using a fashionable term that refers to evidence or compromising material. "It's likely just the beginning."

Investigators caution that they have not yet determined the significance of the Cayman accounts. No one has been charged in the overall investigation, and the Bank of New York has not been accused of any wrongdoing.

The Kremlin declined to comment on reports of offshore bank accounts held by Yeltsin's family.

Earlier this month, Swiss authorities uncovered evidence that Mabetex Project Engineering, a construction company hired by the Kremlin, paid tens of thousands of dollars in credit-card bills for Yeltsin, Tatyana Dyachenko and another daughter, Yelena Okulova.

In Switzerland, investigating magistrate Daniel Devaud said this week that his investigation of suspicious financial transfers by Russian officials -- including the Mabetex payments -- is widening and growing more complex.

Previously, Swiss prosecutors were concentrating on allegations that Mabetex, a Lugano, Switzerland-based construction firm, paid $10 million in bribes in exchange for $300 million in contracts to renovate the Kremlin and other government offices.

Law enforcement sources have said that the gratuities provided by Mabetex included the credit-card payments for President Yeltsin and his immediate family. While he is still interested in Mabetex, Devaud said, "it is not the key point of my investigation. The key point of my investigation is the financial movements appearing in the Borodin affair."

Pavel Borodin is a top associate of Yeltsin who is responsible for administrative affairs at the Kremlin. Among other things, Swiss investigators have alleged that Borodin controlled money that Mabetex transferred to a bank account in Lugano.

Both Mabetex and Borodin have denied any wrongdoing.

In May 1997, Yeltsin signed a decree requiring top Russian officials to disclose their incomes. The decree was signed "with the purpose of developing effective mechanisms of preventing corruption and the abuse of power." When the figures were published for 1997, Yeltsin declared income of nearly $320,000, which included his salary, interest on deposits and royalties from his 1994 book, "View From the Kremlin." Yeltsin's 1997 income was a huge jump from the declared sum of 1996 of $45,000.

Leonid Dyachenko, Yeltsin's son-in-law, heads an oil products trading company, East Coast Petroleum. A subsidiary of East Coast Petroleum, Belka Trading, was involved in a deal to publish Yeltsin's memoirs.

Tatyana Dyachenko became an official Kremlin adviser on June 30, 1997, but her influence goes back earlier. During the 1996 Yeltsin reelection campaign, she was a key link between the political strategists, such as Anatoly Chubais, and the president. After the election, her influence grew as Yeltsin made the difficult decision to undergo heart surgery. By the time she was officially made a Kremlin adviser, the appointment was a formality for a role she was already playing.

Banking Committee Chairman Jim Leach (R-Iowa) said in a statement that the "meaning of today's testimony is that money laundering has gone to the top of the Russian political structure with the confirmation that President Yeltsin's son-in-law is the beneficiary of two accounts in the Cayman Islands' branch of a reputable New York bank." But it is far from clear whether U.S. or Swiss authorities will be able to prosecute a Russian official for money laundering.

The Swiss inquiry appears to be hampered by several factors: the reluctance of Swiss banks to turn over evidence, the division of prosecutorial authority between regions and, most of all, the failure of the Russian authorities to show that the money that Kremlin officials allegedly moved through Swiss banks was illegally obtained.

But the Russians are also somewhat handicapped, because Swiss law gives suspects ample opportunity to delay the release of investigative documents to top prosecutors in other countries.

Bernard Bertossa, the top prosecutor for the Geneva region that is running the money-laundering investigation, said in an interview that he wrote Russian prosecutors about four months ago about what his investigators had found by that point: about 10 Swiss bank accounts, containing roughly $3 million, connected to people tied to the Kremlin.

The Russian formally requested the documentation, but so far the Swiss haven't turned it over. "There are cantonal appeals, federal appeals. It takes months and months," Bertossa said.

If Russian authorities ultimately fail to pursue the evidence, the Swiss may still be able to seize the money in Swiss bank accounts as the apparent profits of a crime. "We may not have enough evidence to prosecute somebody, but enough to seize the money," he said.

Yuri Skuratov, who headed the Russian general prosecutor's office until Yeltsin forced him out this spring, said in an interview last week that he thinks Yeltsin was ignorant of the alleged bribery and money laundering by Kremlin officials.

"I don't know that Yeltsin was in the know of such things," he said. "I believe the president is innocent."

Asked how he explains the gold Euro credit card in the name of Boris N. Elstine, the bills for which were delivered to Mabetex's president, Skuratov answered: "I cannot explain it, even to myself."

O'Harrow reported from New York; LaFraniere reported from Geneva. Staff writer David Hoffman in Moscow also contributed to this report.