Russia's giant Yukos oil company said Thursday that it would "very likely" declare bankruptcy by the end of the year unless Russian tax authorities eased up in a multibillion-dollar case against the company that is fraught with power politics.

The prediction came a day after a Moscow court upheld a $3.4 billion back-tax bill, the first of what executives and analysts expect to be a series of massive penalties against Yukos. Although the firm said it would appeal, analysts held out little hope that it could win in a court system heavily influenced by Russian authorities.

"If the claims we are facing are confirmed by higher courts, the situation will depend on the goodwill of the government to settle," the company's deputy chairman, Yuri Beilin, said at a news conference. "If such goodwill is not there, then without doubt the company will be bankrupt this year."

The statement, the first time the company has formally raised the prospect of bankruptcy, sent Yukos stock tumbling 11.6 percent to $8.40 a share on the Russian trading system index, or RTS market. Once Russia's most successful private enterprise, the company has lost 46 percent of its market value since its chief shareholder, Mikhail Khodorkovsky, was arrested at gunpoint in October on tax and fraud charges.

The unexpectedly quick ruling by the Moscow court late Wednesday came about 36 hours before another court was to convene for the latest hearing in the criminal case of Khodorkovsky. Russia's richest man and a rival of President Vladimir Putin, he has been held without bail for seven months. Russian authorities refused to allow a visiting special envoy from the Council of Europe, an organization of 45 countries based in France, to see Khodorkovsky in prison this week.

Putin last fall said the legal case was focused on Yukos shareholders and not on the company, Russia's second-largest oil producer. But subsequent actions by authorities have targeted the company's assets and raised the possibility of its breakup.

Analysts said the bankruptcy threat was an attempt to up the ante. "It's brinkmanship, that's for sure," said Roland Nash, chief strategist at Renaissance Capital, a leading investment bank here. "They're trying to publicize the seriousness of the situation for the company."

Nash said Yukos's owners might decide that a bankruptcy filing was the best option to protect their assets against the Russian government because proceedings would be held not just in Russian courts but also in international courts because of the company's ownership structure and registration. The Kremlin, by contrast, might want to avoid a bankruptcy case because it could drag on for years and send a negative message to foreign investors, he said.

Christopher Granville, a strategist at another investment bank, United Financial Group, said that a bankruptcy filing did not necessarily mean Yukos would be broken up. Because the Russian government has frozen Yukos's assets, bankruptcy court supervision would be required to raise enough money to pay off the tax debt.

"It would not lead to the liquidation and breakup of Yukos," Granville said, although he acknowledged that more skeptical observers might suspect that the court process would be "simply rigged to strip out assets."

In written statements Thursday, Yukos denied any wrongdoing and complained that the court rubber-stamped the tax claim after hearing three days of arguments from the government and only three hours from the Yukos side.

But Yukos executives seemed resigned to having to pay more. The company disclosed that it had $800 million in liquid funds and expects to have up to $1.2 billion on hand by the end of June. If allowed to pay in installments, it said it could satisfy only 70 percent of the bill for 2000 by the end of this year.