NEWS ANALYSIS : Deepening Differences Chill Climate for Clinton-Yeltsin Mini-Summit : Diplomacy: The two leaders’ meeting in New York comes amid a series of disagreements. Foremost among them is Russian anger at NATO plans to expand.

When Russian President Boris N. Yeltsin sits down today with President Clinton, the background soundtrack for this mini-summit may include the sounds of Russian sabers rattling in a cold autumn wind.

“With every new Russian-American summit, relations between the two Cold War adversaries are becoming chillier,” declared Moscow Times columnist Pavel Felgenhauer.

Today’s summit is already looking more like the icebound meeting between Soviet leader Mikhail S. Gorbachev and President Ronald Reagan in Reykjavik, Iceland, in 1987 than the friendly Clinton-Yeltsin meeting in Vancouver, Canada, in 1993, he said.

The U.S.-Russian relationship is now marred by a growing list of differences on which neither side is likely to give ground: Russian plans to build nuclear power plants in Iran and Cuba; bitter clashes over policy in Bosnia-Herzegovina and Russia’s refusal to put its peacekeepers under North Atlantic Treaty Organization command; a campaign by Republicans in the United States to build a ballistic missile defense system, and, most divisive, Russia’s vehement opposition to NATO plans to expand membership to Central and East European nations.

Yeltsin, in a speech Sunday to world leaders gathered in New York for the United Nations’ 50th anniversary, said NATO’s eastward expansion would “put a barrier in the way to establishing a unified Europe. . . . The strengthening of one bloc today means a new confrontation tomorrow.”

Over the past several weeks, Russian officials have begun threatening specific retaliation if NATO goes ahead with its expansion plans.

In an anonymous but well-orchestrated campaign of leaks to the media, military and intelligence officials have said they may re-aim Russia’s intercontinental ballistic missiles at Poland and the Czech Republic and re-invade the Baltic states if these former Soviet possessions join NATO.

The Russian Defense Ministry says it knows nothing about where these leaks originated. Analysts say the hard-line tactics, reminiscent of Soviet-era propaganda campaigns, are no more than summit-eve maneuvering and Russian election-season politics. The prospect of NATO nuclear weapons based even closer to Russia’s historically vulnerable western border triggers a visceral reaction of fear and resentment, even among Russian liberals, and seems to be one of the few issues that unites the political spectrum here.

But Russian analysts nonetheless warn that the angry posturing should not be ignored.

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“This is bluff, no doubt about it,” said defense expert Alexander A. Konovalov. But if NATO keeps to its present course, he warned, “the bluff may become a reality. It is possible that the United States will have to choose between partnership with NATO and cooperation with Russia.”

Konovalov described the articles as leaks organized by “very secret agencies,” probably with the indirect approval of Defense Minister Pavel S. Grachev and Gen. Mikhail P. Kolesnikov, chief of the general staff, and with the specific intention of frightening the West and the countries seeking membership in the Atlantic security pact.

The threat to re-aim Russian ICBMs at Poland and the Czech Republic appeared earlier this month in the Nezavisimaya Gazeta newspaper, attributed to “a high-ranking anonymous officer” of the main operations department of the general staff.

The officer said Russian military planners believe that if conflict broke out in Europe, Russia’s former Warsaw Pact allies would gladly collaborate with NATO and allow tactical nuclear weapons to be stationed on their soil even if they were not yet NATO members.

The general staff proposes to respond, the officer said, by re-aiming its ICBMs, by creating a military-political alliance with pro-Russian Belarus that would enable it to station a “major military force” on the border with Poland and Lithuania, and by beefing up the armored units on Russia’s northwest border.

A spokesman for the Strategic Rocket Forces, Alexander V. Buchin, said he had no information about such plans, “but such developments are very possible.” Re-aiming the ICBMs at Eastern Europe “will take some technical thinking,” Buchin said, but “it is doable and will not be a difficult problem for us.”

Russia would not be breaking any arms-control pacts by re-aiming its missiles, because last year’s U.S.-Russian agreement to de-target each other does not cover Eastern Europe, said Bruce Blair, a nuclear weapons expert at the Brookings Institution in Washington.

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Blair said, however, that both the United States and Russia are well aware that de-targeting is essentially meaningless because missiles can quickly be aimed anew by means of a computer program that contains the old Cold War targets.

“It takes about as long to get those programs up as it does to change the channels on your TV set,” Blair said. “The idea that we’ve stopped aiming missiles at each other is false. The Russians would take [about] a minute to re-target theirs, and we would take no more than a few seconds.”

The threat to target Poland and the Czech Republic “is basically saber-rattling to warn Poland and the Czech Republic,” Blair said.

The Baltic nations reacted with alarm to an unattributed report in the Komsomolskaya Pravda newspaper that Moscow was drawing up contingency plans for a preemptive invasion if the tiny former Soviet republics are admitted to NATO. Defiant, the leaders of Estonia and Latvia responded by telling the West that such threats are exactly why they need protection under NATO’s umbrella, and the sooner the better.

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There is no evidence that the Kremlin has approved such radical plans, but it has not disavowed them. The new willingness to brandish such threats suggests that key powerbrokers in Moscow no longer believe that the West will listen to a weakened Russia unless it sees a credible military menace.

Last week, Yeltsin warned that Russia may also stop reducing its arsenal of strategic nuclear weapons if the United States acts on a U.S. Senate vote last month to develop an antiballistic missile system to protect the country from a surprise attack by a “pariah” state.

“If such a mood becomes the official line of the United States, strategic stability would without doubt be blown up,” Yeltsin told the Guardian newspaper in Britain. The ABM treaty, which strictly limits defensive missiles on both sides, is the basis for the START I and START II treaties that call for deep cuts in both countries’ offensive arsenals.