* Pact to set new limits for Russian, U.S. nuclear arsenals
* Boost for both sides and for ties, but disputes linger
* Ratification by lawmakers in both countries required
(Updates with Russian comment)
By Steve Gutterman
MOSCOW, April 2 (Reuters) - The U.S. and Russian presidents
are to sign a pact on Thursday committing the former Cold War
foes to unprecedented nuclear arms reductions, cementing a
hard-won deal that should put strained ties on firmer footing.
After nearly a year of tough negotiations, the signing by
Barack Obama and Dmitry Medvedev in Prague, the capital of a
former Soviet satellite now in NATO, will symbolise cooperation
between Washington and Moscow for the sake of global security.
Both presidents say new cuts in the largest arsenals on the
planet are a step toward a world without nuclear weapons and a
signal to nations seeking them that there is no need.
But the successor to the 1991 Strategic Arms Reduction
Treaty (START I) will not come into force without ratification
by lawmakers in both countries, and could face a rough ride in
the U.S. Senate.
Analysts say it will be no cure-all for Russian-American
relations, which have improved after hitting a post-Soviet low
during Russia's 2008 war with Georgia but remain troubled by a
range of disputes.
Neither will the START successor deal resolve simmering
tension over missile defence, which has haunted ties since the
Reagan era and hurt them badly in the past decade.
With Russia saying it could withdraw from the pact if its
security is threatened by U.S. missile defences, the divisive
issue could come to the fore again.
Russia has long complained that cutting its offensive
arsenal could leave it exposed if the United States builds a
missile shield in Eastern Europe. Prime Minister Vladimir Putin
clouded hopes for the offensive weapons pact by suggesting in
December that it should also limit missile defences.
The pact is expected to acknowledge a link between offensive
and defensive weapons, but U.S. officials have stressed it will
not restrict the development of missile defences.
The United States says its defensive plans are no threat to
Russia.
The Kremlin's top foreign policy adviser, Sergei Prikhodko,
said on Friday that Russia would underscore its right to bow out
of the pact in response to U.S. missile defences in a unilateral
declaration alongside the treaty, Russian news agencies
reported.
FOREIGN POLICY
Moscow's concerns about missile defence and Western
conventional weapons superiority also mean further nuclear arms
agreements Obama hopes can follow will be far harder to secure.
"It took 10 months, but this treaty is going to be fairly
easy compared to the next one," said Steven Pifer, a senior
fellow at the Brookings Institution.
Negotiators missed an initial target of Dec. 5, when START I
expired, and failure still seemed possible until both sides
announced late last month that Obama and Medvedev would meet in
Prague on April 8 to sign the pact.
The treaty would limit the number of operationally deployed
nuclear warheads to 1,550 for each country -- down nearly
two-thirds from START I and 30 percent lower than the ceiling of
the 2002 Moscow Treaty set for each side by 2012.
The signing will be the first major concrete foreign policy
achievement for Obama, who has sought to "reset" Russia ties.
It will pave the way for a nuclear security summit he is
hosting the following week -- hoping to marshal broader support
in standoffs with Iran and North Korea -- and a May conference
meant to bolster the global nuclear Non-Proliferation Treaty.
But there is no guarantee it will translate into stronger
Russian backing for U.S. policy on Iran and Afghanistan.
"Agreeing a strategic arms treaty is a big achievement, but
it does not automatically carry over into other aspects of
relations," said Fyodor Lukyanov, editor of the journal Russia
in Global Affairs.
Signing a major nuclear weapons treaty is also a boost for
Medvedev, still in Putin's shadow. The pact with the United
States will remind the world of Russia's nuclear might.
And it is in the Kremlin's interest because Russia's aging
arsenal would likely drop to the limits set by the treaty in
several years anyway, analysts say.
But the signing will leave one crucial hurdle: ratification.
Even without limits on missile defence, which would have
ruined the treaty's chances in the Senate, Obama may have
trouble securing the 67 votes needed -- particularly if the
process drags on beyond November elections in which his
Republican foes are expected to pick up seats.
The Kremlin faces no such challenge from Russia's docile
parliament. But Moscow has urged "synchronised" ratification,
hinting it will hold back until Senate support is assured.
"Russia is ready to ratify the treaty, but Russia absolutely
does not want to find itself in a position where it ratifies and
the Senate does not," Lukyanov said.
(Additional reporting by Matt Spetalnick; editing by Myra
MacDonald)
