The bankruptcy auction of a Siberian oil company today intensified a fresh conflict over the riches of the former Soviet Union that continues to force foreign investors to the sidelines.

The oil company Chernogorneft, which sits astride the northern part of the huge Samotlor oil field in western Siberia, was sold to Tyumen Oil Co. for $176 million. Tyumen, Russia's sixth-largest oil company, already controls the southern part of the Samotlor field. The auction was held in the city of Nizhnevartovsk, about 1,600 miles east of Moscow.

The sale triggered howls of protest from the owners of Chernogorneft's parent company, Sidanco. They said the bankruptcy process was flawed and the auction unnecessary, and earlier had filed suit in New York and Russia in an attempt to stop the sale.

Among those contesting the sale are BP Amoco PLC, which invested half a billion dollars in Sidanco in 1997, and the Sputnik Fund, an investment fund run by financier Boris Jordan, which includes investments by George Soros and the Harvard Endowment.

The investors have said the Chernogorneft sale is another key test case of whether Russia will protect foreign investors. While direct foreign investment in Russia was never huge during the boom years of 1997 and 1998, it now has slowed to a trickle. One reason, analysts said, is the lack of protection for minority shareholders and foreign investors.

Russia also has some of the world's worst credit ratings after last year's default on its domestic debts. This has made it even more difficult for Russian firms, which need capital to restructure, to attract overseas loans and capital.

In London, the European Bank for Reconstruction and Development issued a statement tonight calling the bankruptcy auction "a sham" and "wholly contrary to the concepts of fairness and transparency" that "could have severe repercussions on the investment climate in Russia." Justice, the bank said, "has been perverted."

Sidanco was one of the vertically integrated oil majors carved out of the state-owned Soviet oil industry, and it was bought in 1995-96 by the Russian tycoon Vladimir Potanin and his allies through a series of controversial auctions at rock-bottom prices.

However, Sidanco now is falling apart, with key production units being bankrupted and sold off at auctions. Sidanco's owners have accused Tyumen of foul play in the courts in making a bid for the oil production units, which Tyumen denies.

Despite the protests and lawsuits, the bankruptcy sale of Chernogorneft went ahead as scheduled, and Tyumen was announced as the winner by the Russian Federal Property Fund. The winning bid of $176 million is but a fraction of the annual value of the company's production of 125,000 barrels a day of crude oil, worth about $1.1 billion at current world oil prices.

BP Amoco, which holds 10 percent of Sidanco, called the bankruptcy process "seriously flawed" and said it was reviewing its future in Russia as a result. On Thursday BP Amoco said it believed the tender was illegal and that Chernogorneft was a viable, profit-making company.

Potanin's holding company, Interros, which owns 40 percent of Sidanco, also protested the sale today, saying it "was conducted in an atmosphere of unprecedented pressure on the court system."

Tyumen President Simon Kukes replied to the criticism by saying "it is critical for the Russian oil industry to remain . . . friendly to foreign investments." He said the oil company "is prepared to enter into a long-term strategic alliance" with BP Amoco and other investors that "would ensure that these investors do not suffer a loss from the sale of Chernogorneft." He did not offer details.

Tyumen is jointly owned by one of Moscow's leading oligarchs, Mikhail Fridman of Alpha Bank, and New York-based Access Industries Inc., which is seeking $489 million in U.S. Export-Import Bank credits.