WASHINGTON (Reuters) - President Barack Obama urged Russia on Tuesday to work with the United States to "update" a decades-old agreement on dismantling nuclear and chemicals weapons that is set to expire in mid-2013.

Russian Deputy Foreign Minister Sergei Ryabkov said in October that Moscow intended to end the 1992 agreement, the latest sign that the much-vaunted "reset" in relations between the Cold War-era foes may be running out of steam.

Obama, attending a conference of nuclear anti-proliferation experts at the National War College in Washington, took note of Moscow's complaints and expressed optimism the pact would be extended.

"Russia has said that our current agreement hasn't kept pace with the changing relationship between our countries," Obama said. "To which we say, 'let's update it.'"

"Let's work with Russia as an equal partner. Let's continue the work that's so important to the security of both our countries. And I'm optimistic that we can," he said.

The project has been extended twice, most recently in 2006. U.S. officials say it has helped to deactivate more than 7,650 strategic warheads, neutralized an unspecified number of chemical weapons, safeguarded fissile materials and mitigated biological threats.

Ryabkov was quoted by Russia's Interfax news agency on October 10 as saying that "the agreement doesn't satisfy us, especially considering new realities." The State Department said at the time that Washington and Moscow were still talking about the pact, which expires in June 2013.

Russia's Foreign Ministry had suggested that cooperation could continue but under different rules.

Bilateral agreements including the latest START nuclear arms treaty, put in force in February 2011, built the foundation for the U.S.-Russia "restart" initiated when Obama took office in 2008 - and which the White House considers one of his top first-term foreign policy achievements.

But recently ties have been strained, most notably by Moscow's decision to close the office of the U.S. Agency for International Development in Moscow and by deep differences over how to deal with the civil war in Syria, a Russian ally.

(Reporting By Matt Spetalnick; Editing by Vicki Allen)