That final 5 percent sure seems to be causing a lot more trouble than anyone expected.
Last month, Russian President Dmitry Medvedev told journalists that negotiations to frame the first major post-cold war Strategic Arms Reduction Treaty (START), begun between the US and Russia amid great optimism a year ago and slated to be finished by the end of 2009, were "95 percent complete."
But on Thursday, Secretary of State Hillary Clinton emerged from a long afternoon of talks with her Russian counterpart, Sergei Lavrov, to say "don't count your chickens before they hatch," when asked when the treaty, intended to radically slash US and Russian offensive nuclear arsenals, would be ready for signing.
She added that negotiators have made "substantial progress" and said she hoped the document will be finalized soon.
"The work may not be going as fast as expected, but there is a strong commitment on the part of both presidents to get it done" before the conference opens, says Mikhail Margelov, chair of the foreign affairs commission of the Federation Council, Russia's upper house of parliament. "We're already preparing to move toward ratifying the treaty in parliament, after the presidents have signed it," he says.
On Friday, Mrs. Clinton is expected to sit down with Medvedev, and later with former president Vladimir Putin, for discussions in which START is expected to figure heavily.
Experts say that the treaty, which was intended to be the centerpiece of a reinvigorated US-Russian relationship, has been bogged down in quarreling over the issue of missile defense. Many hoped that issue had been laid to rest after Mr. Obama shelved a Bush-era plan to station antimissile interceptors in Poland last September.
The new deal would probably set a limit of 1,600 strategic warheads on each side, roughly a 25 percent reduction from current levels. That would be the smallest number of nuclear weapons that Russia and the US have aimed at each other – once known as the "balance of terror" – since the nuclear arms race got serious in the 1960s. The number of delivery vehicles – missiles and bombers – would also be sharply reduced.
But Russian negotiators have raised doubts about continuing US plans to station short-range antimissile systems in Romania and Poland during the 10-year period that the new treaty would cover. Many Russian conservatives have complained that without stiff controls on defensive weapons, US antimissile technology may render Russia's nuclear arsenal obsolete within a few decades.
Boris Gryzlov, speaker of Russia's lower house of parliament, the State Duma, and a close political ally of Mr. Putin, told journalists this week that the new treaty would have to contain tough language linking the need to limit defensive weapons with any reductions of offensive missiles. "Without that, there is no chance the treaty will be ratified in the Duma," Mr. Gryzlov said.
Last December, now-Prime Minister Putin broke the confidentiality of the START negotiations to publicly complain about US missile defense plans, raising questions about a possible Kremlin split over the wisdom of finalizing the treaty at all.
During a visit to Moscow last July, Mr. Obama acknowledged Moscow's concerns over the potential threat a US-controlled antimissle shield might pose to Russia's aging nuclear deterrent, but stopped short of agreeing to bring back a special treaty to ban such weapons.
Cold war-era nuclear arms control got seriously under way only after the two sides signed the 1972 Anti-Ballistic Missile Treaty, curtailing work on antimissile systems. But President George W. Bush unilaterally withdrew from the ABM treaty in 2001, throwing US-Russian strategic relations into a tailspin.
Experts say the two sides will likely paper over the rift with a declaration linking the problems of controlling offensive and defensive weapons, but push any accord limiting antimissile systems into the future.
"The logic of the US position is not to have its hands tied by any restrictions on defensive weapons," says Alexei Pushkov, head of the Institute of Contemporary International Problems, a think tank that advises Russia's Foreign Ministry. "We already know that this treaty will not solve the problem that development of offensive and defensive weapons are closely linked. They may have a declaration acknowledging it, but so what? It means we will face this question down the road."