MOSCOW - President Barack Obama and Russian leader Dmitry Medvedev on Monday agreed a target of cutting vast Cold War arsenals of deployed nuclear warheads by around a third from current levels to 1,500-1,675 each.

The pledge by Obama and Medvedev puts the world's two biggest nuclear powers further along the path to finding a replacement for the landmark 1991 Strategic Arms Reduction Treaty (START-1) which expires on December 5.

But the cuts announced on Monday only take the United States and Russia 25 operationally deployed warheads below a range of 1,700-2,200, which both sides had already committed to reach by 2012 under the 2002 Moscow Treaty.

After the cuts -- which have to be made within seven years of a new treaty taking force -- the United States and Russia will still have enough firepower to destroy the world several times over. Many hurdles remain to finding a replacement to START by December.

Russia and the United States are still haggling over what exactly constitutes a nuclear weapon and the Kremlin is deeply opposed to U.S. plans for a missile defense system in Europe.

NUCLEAR CUTS

Finding agreement on a replacement for START-1, signed by George Bush and Mikhail Gorbachev just months before the close of the Cold War, is seen by both sides as a way to reset relations after the friction of recent years.

Presidents Obama and Medvedev agreed at their first meeting in London on April 1 to pursue new reductions to strategic nuclear weapons and instructed negotiators to begin talks on a replacement for START-1.

This was already a step forward because Obama's predecessor George W. Bush showed little interest in a successor treaty to START-1, arguing that it was not necessary. Obama, however, has made nuclear disarmament a priority.

The cuts announced on Monday came after negotiators worked through the weekend to get a deal for the presidents to sign, diplomats said.

It's better to be talking than fighting but there's a lot of talking to go, said John Isaacs, executive director of the Center for Arms Control and Non-Proliferation in Washington.

The basic flavor is they've made some progress but not many concrete results. President Bush messed up a lot of things but it will take more than eight months to fix, he said.

It will take a while to get to the really deep cuts in warheads and it will take another agreement after this one.

Officials say an agreement on a START treaty that slashed nuclear weapons would help Washington and Moscow to set an example to other countries ahead of talks next year on revising the Non-Proliferation Treaty (NPT).

But Russia and the United States still currently hold 95 percent of the world's nuclear warheads.

MISSILE DEFENSE
Russia is deeply opposed to U.S. plans to station anti-missile 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.

The Kremlin says the U.S. anti-missile system is closely linked to START negotiations and Moscow wants a resolution on missile defense before agreeing to a concrete deal on a replacement for START.

Washington says the system is intended to protect the United States and its allies against a possible Iranian missile attack but Russia argues that the system could be used against its nuclear arsenal as well.

Obama and Medvedev seemed on Monday to have moved away from the rhetoric on missile defense that sometimes soured relations between Washington and Moscow.

Medvedev said that missile defense was not a threat while Obama said any discussion on the issue had to include talks on offensive and defensive weapons, a key Kremlin demand over previous months.

I believe that over time we will end up seeing that the U.S., Russian positions on these issues can be reconciled and that in fact we have a mutual interest in protecting both our populations, Obama said of missile defense.

(Additional reporting by Conor Sweeney, Editing by Myra MacDonald)

Russia George W. Bush Dmitry Medvedev Barack obama