The Bush administration is holding out the incentive of a $10 billion project for Russia if it would stop helping Iran develop potent missiles and weapons of mass destruction.
The potentially lucrative deal involves storage of radioactive material from around the world.
"If the Russians end their sensitive cooperation with Iran, we have indicated we would be prepared to favorably consider such transfer arrangements potentially worth over $10 billion to Moscow,'' the State Department said.
A tradeoff could resolve one of the most difficult issues in an overall good relationship between President Bush and Russian President Vladimir Putin.
They will meet this weekend in Mexico at a conference of leaders of Asian and Pacific nations.
Undersecretary of State John R. Bolton was sent to Moscow in advance of the meeting to discuss U.S. concerns about Russia's assistance to Iran.
Bolton has talked to top Russian officials about the problem several times in the past without apparent results.
Specifically, the administration wants Russia to halt construction of a light-water nuclear reactor at the Iranian coastal city of Bushehr.
Russia has denied consistently it is helping Iran develop nuclear weapons or its missiles program.
"The U.S. position is clear,'' the State Department said. "A weapons of mass destruction-armed Iran would be a major threat to Russia as well as to the United States and our friends and allies in the region.''
Hinting that Bush will take the issue up with Putin, the statement said, "We will continue to intensively work this issue closely at senior levels with Russia.''
An end to aiding Iran would benefit the U.S.-Russian relationship and help Russia "economically, politically and strategically far more than any short-term gain from sensitive transfers to Iran,'' the statement said.
The United States controls whether spent fuel from reactors in other countries can be transferred to Russia for storage because it originally provided the fresh fuel to the countries.
Russian Atomic Energy Minister Alexander Rumyantsev, who met with Bolton in Moscow, said afterward on Ekho Moskvy radio that "Russia is not providing any weapons technologies and is not even negotiating such projects with Iran.''
Also on Wednesday, Bush signed into law the Russian Democracy Act, which authorizes — but does not actually provide — U.S. foreign aid to Russia for "the promotion of democracy, rule of law, international exchanges, human rights, economic reforms, administration of justice and the development of a free and independent media in Russia.''
Rep. Tom Lantos, D-Calif., who sponsored the legislation, said it would help Russia as it transitions to a democratic society and adopts a free market economy.