MOSCOW Washington hopes that by backing away from an anti-missile system in east Europe, it will get Russian cooperation on everything from nuclear weapons cuts to efforts to curb Iranian and North Korean nuclear ambitions.
But will Moscow keep its side of the bargain?
The U.S. move on the shield -- due to be announced later on Thursday but already flagged by Czech and Polish officials -- removes at a stroke the biggest outstanding obstacle to bilateral relations between the former superpowers and will be hailed by the Kremlin as a big victory.
Russia's leaders have fiercely resisted the missile shield, saying it would upset regional security because it could be used to neutralize Moscow's vast nuclear arsenal.
Ignoring U.S. assurances that the system was not targeted at Russia, President Dmitry Medvedev threatened last year to station missiles in a Russian enclave near Poland if the United States implemented the plan.
With the shield now on the back burner, both sides believe a deal cutting long-range nuclear arsenals can be inked this year and Russia has already agreed to allow U.S. military cargos to transit across its vast territory en route to Afghanistan.
But the shield's demise in its originally planned form may also have unintended consequences in the former Soviet bloc.
Russian diplomacy is largely a zero-sum game and relies on projecting hard power to force gains, as in last year's war with Georgia over the rebel regions of Abkhazia and South Ossetia or the gas dispute with Ukraine at the start of this year.
Western concepts of "win-win" deals and Obama's drive for 21st century global partnerships are not part of its vocabulary.
Diplomats here say Moscow hardliners could read the shield backdown as a sign of Washington's weakness. Far from doing the bidding of the United States, they may instead press for further gains to shore up Russian power in the former Soviet bloc.
Ukraine, Georgia and other Kremlin foes in the ex-Soviet Union may be the first to feel the consequences.
Poland and the Czech Republic are also nervous. In Warsaw, the timing of the U.S. move is particularly delicate as it coincides with the 70th anniversary of the Soviet invasion of eastern Poland.
Analysts are particularly concerned about Ukraine, which faces a presidential election next January. Most of Russia's vast gas exports flow through its territory and the country reluctantly hosts a large Russian naval base.
Russia has already rebuked Kiev for its "anti-Russian" stance and refused to deal with President Viktor Yushchenko, tactics which recall those used with Georgia in the period leading up to last year's war.
Diplomats cite the Crimean peninsula -- Russian territory until the 1950s and home to Moscow's Black Sea fleet as well as thousands of Russian passport-holders -- as one potential flashpoint.
In a sign of the level of concern, one senior Western envoy here privately estimated the chances of a Russian military intervention in the Crimea over the next year at 50-50.
Georgia could be another tinder box.
Moscow has made no secret of its disappointment that its implacable foe President Mikheil Saakashvili remains in power, despite months of opposition protests and his defeat in last year's war.
But with plenty of troops and heavy weapons stationed in South Ossetia, less than 100 km (60 miles) from the Georgian capital, Russia is in a potentially strong position to deal with its "unfinished business" in Georgia if it so chooses.
The shifting U.S. position is already unnerving some of the pro-Western countries in the former Soviet bloc.
Ex-communist states have already noticed that the unwavering support provided to them by the Bush administration and its tough rhetoric against Russia has been replaced in Washington by a more pragmatic, conciliatory stance.
In an open letter to Obama in July, senior figures from central and eastern Europe urged the U.S. leader not to be swayed by Russian objections when he made his decision on the missile shield.
But the missile shield rethink is a central tenet of the "reset" strategy deployed by President Barack Obama on relations with Russia and promoted during his first visit to Moscow in July.
Obama went out of his way to praise Medvedev during his visit, spending a total of eight hours with him against only two for Vladimir Putin. He criticized Putin before his visit as a man with one foot stuck in the past, contrasting him unfavorably with Medvedev.
The missile shield move marks another attempt by Obama to shore up what Washington sees as a more liberal, pro-Western strand in the Russian government personified by Medvedev.
But with hardliners increasingly in the ascendant in Moscow, and Putin openly talking about returning to the top Kremlin job at the next election, it is far from clear whether Russia's next international moves will be the ones Obama intended.