President Boris Yeltsin, visiting China to secure support for Russia's military campaign in Chechnya, launched a surprising verbal assault on President Clinton today, including a blunt reminder that Russia is a nuclear power.

Midway through a series of meetings with senior Chinese leaders, who greeted the Russian president with bear hugs and warm smiles, a stern-sounding Yeltsin called reporters to attention and assailed Clinton for criticizing Russia's tactics in Chechnya earlier this week.

"Yesterday, Clinton permitted himself to put pressure on Russia," Yeltsin said ahead of talks with Li Peng, China's most conservative and anti-Western leader. "It seems he has for a minute, for a second, for half a minute, forgotten that Russia has a full arsenal of nuclear weapons. He has forgotten about that."

While members of the Russian government have expressed resentment at what they view as interference from the West, the sight of Yeltsin launching a direct attack on Clinton marked an escalation of rhetoric at a sensitive moment in relations between the two countries, analysts said.

Chinese President Jiang Zemin told Yeltsin that he "completely understood and fully supported Russia's actions in combating terrorism and extremism in Chechnya," according to Russian Foreign Minister Igor Ivanov. Chinese spokesman Zhang Qiyue added that China "understands and supports the efforts made by Russia in safeguarding national unity and territorial integrity."

In an additional swipe at the U.S. president, Yeltsin said: "It has never been the case, and will not be the case, that he alone dictates to the world how to live, how to work, how to rest and so on. No, and again no. Things will be as we have agreed with Jiang Zemin. We will be saying how to live, not he alone."

In Washington, Clinton continued his criticisms of Russia's actions, largely dismissing Yeltsin's complaints.

"I don't think what they're doing will help them to achieve their goal" of defeating Chechen rebels, the president told reporters at the White House. "I don't think displacing hundreds of thousands of civilians will achieve that goal."

Clinton said the United States has not forgotten that Russia remains a nuclear power.

"I didn't think he'd forgotten that America was a great power when he disagreed with what I did in Kosovo," Clinton said. "I mean, we can't get too serious about all the--let's not talk about what the leaders are saying and all these words of criticism."

In Moscow, Prime Minister Vladimir Putin played down Yeltsin's remarks, arguing that it would be wrong to conclude from the president's statements that relations between Russia and the United States were souring. Officials traveling with Yeltsin, however, did not immediately seek to play down the president's statements, as they have in the past when the volatile Russian leader has made startling statements.

On Monday, Clinton sharply criticized a Russian ultimatum to residents of Grozny, the capital of Chechnya, to flee by Saturday or face annihilation. Russia's military has used air power and heavy artillery in its campaign against separatist rebels in the north Caucasus region, resulting in a high civilian death toll and a massive exodus. Many Russians view the war as a fight against terrorism following a series of apartment house bombings in Russia that killed nearly 300 people, and armed incursions by Chechnya-based Islamic rebels into the neighboring region of Ingushetia.

Clinton said "Russia will pay a heavy price for those actions, with each passing day sinking more deeply into a morass that will intensify extremism and diminish its own standing in the world." On Wednesday, he added that the United States might work to block International Monetary Fund loans to Russia because of the bombardment.

Russian authorities have since asserted that the ultimatum was a warning directed at the rebels, not civilians, but many of the thousands of civilians in the capital are physically infirm or too afraid of being hit in the cross-fire to try to move through a "safe passage" set up by the military.

In addition to their angry differences over Chechnya, the two former Cold War rivals are involved in a number of other important disputes. Russia adamantly opposes a U.S. proposal to amend the 1972 Anti-Ballistic Missile treaty to allow for a limited missile defense system that would counter attacks from "rogue" nations such as Iraq. The two nations are also involved in a budding conflict over espionage in each other's capitals. U.S. agents arrested a Russian diplomat accused of spying Wednesday, just nine days after an American was detained on similar charges in Moscow.

The raw tone of Yeltsin's remarks, and the fact that he made them in Beijing while talking with Chinese leaders about strengthening strategic ties, offered a jarring contrast to periods of rapport between Clinton and Yeltsin, which have cooled at times in recent years as Russia's great-power status crumbled. Bilateral ties were frayed further over the expansion of NATO and by the U.S.-led air war against Russia's fellow Slavs in Yugoslavia, which Yeltsin reportedly said in April could lead to war in Europe or "maybe even a world war" if Russia became involved.

"There's a real hardening of the Russian position toward the United States and the West in general," said Theodore Postol, an arms control expert at the Massachusetts Institute of Technology who recently met with senior military officials in Moscow.

NATO's expansion in eastern Europe and the war over Kosovo raised suspicions among average Russians about Washington's interventionist intentions, Postol said. Moreover, elites in Russia's foreign policy and security establishment have been alarmed at recent U.S. steps that could lead to the deployment of a national missile defense system, he added.

Russia and China both supported a U.N. resolution against the U.S. proposal, and Yeltsin consulted with his Chinese counterparts on the issue again today in an effort to turn up the heat.

"The two sides had a common stance on the anti-missile defense program," said Ivanov. "Russia and China agreed to safeguard nonproliferation treaties and maintain the global strategic balance. If the U.S. is trying to destroy this system, then it will . . . lead to the proliferation of weapons of mass destruction."

Yeltsin eagerly shook hands with Chinese leaders during his meetings today and smiled broadly to show his vitality. He arrived in China just three days after emerging from the hospital, where he was treated for pneumonia. His outburst on Clinton overshadowed a number of agreements signed by the two sides today, including an important pact ending long-standing border disputes.

Staff writer Charles Babington in Washington contributed to this report.