Building a joint asteroid defence system was not a "real proposal" until the project has funding, which is not on the cards with either country, said US Acting Under Secretary for Arms Control and International Security, Rose Gottemoeller.
The meteorite issue became a global topic after a celestial body exploded over the Russian city of Chelyabinsk in February, injuring 1,500 people.
Meanwhile, Washington hopes to convince Russia to continue slashing strategic nuclear arms, Gottemoeller said on Ekho Moskvy radio.
The New START nuclear arms treaty, signed by Russia and the US in 2010, limits deployed nuclear missiles and bombers capable of carrying nuclear weaponry for each country to 700.
Russia would consider further cuts to its nuclear arsenal if it gets guarantees that US plans to build a missile defence shield in Europe pose no threat to Russia's strategic parity with the US, Chief of Russian General Staff Valery Gerasimov said.
The missile defence shield is a "slightly artificial" issue that Washington hopes to resolve, Gottemoeller said on Ekho Moskvy.
She reiterated the official US position that the shield would not affect Russia's nuclear capabilities.
Washington also hopes to draw on Moscow's vast experience concerning Afghanistan ahead of the US troops' pullout of the country in 2014, Gottemoeller said.