ANALYSIS: Russia-U.S. nuclear arms pact faces tricky hurdles

MOSCOW (Reuters) - Last April, the U.S. and Russian presidents set out to cut the world's largest nuclear arsenals, aiming to agree a new pact before the last major Cold War arms reduction treaty expired on December 5.

Ten months and a missed deadline later, both sides say they expect agreement soon on a replacement for START I - but there's still no deal.

Further delay would amplify questions about a much-trumpeted "reset" in Russian-U.S. relations and cloud the prospects for further arms reductions. It would also send a worrying message to the world's other nuclear or near-nuclear states.

With those concerns in mind, Washington and Moscow are pressing for an agreement before a global conference on nuclear proliferation begins in late April.

Top U.S. officials were in Russia for fresh talks this week and U.S. ambassador to Moscow John Beyrle suggested a new pact would be ready in the "very near future."

Russian Foreign Minister Sergei Lavrov said agreement could be reached soon, though some other Moscow officials are privately less optimistic.

Hurdles to a pact include domestic politics in both countries and differences in their nuclear forces.

Meeting in July, U.S. President Barack Obama and Russian President Dmitry Medvedev agreed the new treaty should cut the number of deployed nuclear warheads on each side to between 1,500 and 1,675.

The target range for the missiles, submarines and bombers that carry warheads was far broader, with the United States wanting to allow 1,100 and Russia -- which has fewer delivery vehicles but plenty of warheads -- calling for a ceiling of 500.

A replacement for START is crucial for Obama initiatives from mending relations with Russia to moving toward a world without nuclear weapons.

Moscow's considerations are more pragmatic. Its aging nuclear arsenal may drop below 1,500 warheads in 5-6 years anyway, experts say, so the Kremlin wants similar limits on the U.S. stockpile.

The sides are near agreement on the numerical limits, though Russia is concerned about the U.S. fleet of submarines that can carry nuclear weapons and wants those ships in a new treaty.

But officials have indicated the most difficult disputes have been over verification measures, which Russia wants to be much less strict than under START.

One of the thorniest issues is access to the telemetry (remote monitoring) data on the flight of missiles being tested, which START forbade either side to hide from the other.

Russia thinks it has got a raw deal out of such rules: they gave Washington information on new Russian weapons while providing Moscow with little in return because the United States has been updating existing missiles, not building new ones.

During a holiday break in talks, Russian Prime Minister Vladimir Putin said if the United States wanted telemetry on Russia's strategic launches it must give Russia data on U.S. anti-missile systems -- a bombshell because a treaty encompassing missile defense would have no chance of ratification in the U.S. Senate.

Some analysts said Putin's remarks sparked speculation he wants to deny Medvedev the prestige of forging a landmark pact. Others said Putin and Medvedev were playing good cop-bad cop and predicted Russia would not push hard on missile defense.

Even an agreed draft treaty is not guaranteed the 67 votes needed for ratification by a Senate wary of Russia's intentions. Obama's Democrats lost one of their 60 seats last Tuesday.

A ratification vote has the "potential to become a referendum on Russia" and its level of support for the United States on issues such as Iran's nuclear program, said Andrew Kuchins, Director of the Russia and Eurasia Program at the Center for Strategic and international Studies in Washington.

Russia's leaders face no such problem with the lockstep lawmakers in the State Duma. But concerns the Senate might reject the pact could give the Kremlin cold feet.

Medvedev warned last week that if Russia and the United states do not ratify the treaty simultaneously, "this process may fail to take place."

(Editing by Michael Stott and Matthew Jones)