MOSCOW (Reuters) -- U.S. and Russian negotiators have still not reached agreement on cutting stocks of their deadliest nuclear weapons ahead of President Barack Obama's first visit to Moscow on July 6, sources close to the talks said.
Obama and his Russian counterpart Dmitry Medvedev are expected to announce next week an outline deal on reducing the numbers of strategic nuclear missiles as the centerpiece of the U.S. president's visit.
The two leaders would sign a framework agreement and then instruct negotiators to produce a detailed treaty ready for signing by December, when an existing pact known as START I regulating the number of long-range nuclear weapons expires.
But Moscow has still not indicated what figure it will settle for, the sources said.
"The reason you haven't seen any firm figures about cuts is that the negotiations are still going on," one senior source close to the process said.
"We are unlikely to know before [July 6] what the Russians will agree to and we may only find out when Obama gets to the Kremlin." Obama is due to meet Medvedev for talks at the Kremlin on the afternoon of July 6.
U.S. officials are still confident of securing an outline arms deal, as well as Moscow's assent for convoys of lethal U.S. military equipment bound for Afghanistan to cross Russian territory, but any agreements may yet be torpedoed by the bitterly fought issue of missile defense.
Washington plans to station antimissile batteries and radar detection systems in the Czech Republic and Poland as part of a global system to spot and shoot down hostile enemy rockets before they reach the United States.
Moscow, which relies heavily on nuclear weapons for its defense because of the poor state of its conventional weapons, fiercely opposes the antimissile system as a threat to its security.
"There can be no real progress in the sphere of nuclear disarmament if it is undermined by the unilateral deployment of a global missile defense system," Anatoly Antonov, the Russian chief arms negotiator, told a conference in Moscow on July 3.
Kremlin sources have said that Obama has shown less interest in pursuing the antimissile plans than his predecessor George W. Bush and that Moscow was encouraged by the United States showing a greater understanding of its concerns.
The Obama administration ordered a review of the antimissile system after taking office and has not yet taken a final position on whether to deploy it.
In the meantime, Russia is bargaining hard on the technical details of how many operational nuclear warheads each side should be allowed and how many "delivery vehicles" -- missiles or bombers -- they could have.
Neither side will comment officially on the details of the talks but the Russian daily "Kommersant" reported on July 3 that the United States was proposing a maximum of 1,500-1,600 operational warheads for each side and 1,100 delivery vehicles.
Medvedev and the commander of Russia's nuclear forces have previously said they were willing to cut warheads to 1,500 and to reduce delivery vehicles substantially, but "Kommersant" said the Russian military was now only willing to accept a limit of 1,700 warheads.
Estimates of current nuclear stockpiles differ but according to the U.S.-based Bulletin of the Atomic Scientists at the start of 2009 the United States had around 2,200 operationally deployed strategic nuclear warheads and Russia around 2,790.
The two sides have already agreed under a 2002 pact known as the Moscow Treaty to limit their arsenals to 1,700-2,200 operationally deployed warheads by 2012.
Experts have criticized this agreement because the reductions are not required to be permanent, warheads may be kept in storage, there is no verification regime to check on compliance, and the treaty expires in 2012.