A senior U.S. official in Moscow says an agreement between Russia and the United States on reducing nuclear weapons stockpiles may not be ready in time for the May presidential summit.

Undersecretary of State John Bolton said Russia and the United States may fail to reach a nuclear arms reduction agreement before a planned presidential summit in May.

Russian President Vladimir Putin and President Bush have both said they want to reduce their nuclear stockpiles to between 1,700 and 2,200 weapons each. Negotiators hoped that a new arms agreement would be the centerpiece of the summit in Russia.

But during a Moscow news conference, Under Secretary of State Bolton said an agreement may not be ready in time. "We have a number of difficult issues," he said. "Questions of how exactly to account for the offensive strategic warheads, measures of transparency and verification and a series of issues that still need to be resolved."

Mr. Bolton met with Russian Foreign Minister Igor Ivanov to discuss the coming summit and the arms agreement.

Moscow has objected to an earlier U.S. announcement that it would like to dismantle some nuclear weapons instead of completely destroying them.

Moscow would also like a legally binding document on the reductions, something President Bush has opposed in the past. But Mr. Bolton says President Bush has changed his mind and would agree to a legally binding document within certain limits.

Mr. Bolton said another issue in the talks is Russian cooperation with Iran on their nuclear program and the sale of Russian missile technology. "Ultimately, it is not a question of what we say," said John Bolton. "But it is a question of Russian national interest. How could any Russian citizen see any benefit whatever in a nuclear equipped ballistic missile capable Iran?"

Russia is Iran's largest arms supplier and has wide-ranging political and economic ties with the Islamic republic. Russia also is helping Iran build a nuclear reactor.

President George Bush included Iran in the so-called "axis of evil," countries that include Iraq and North Korea. The United States considers them sponsors of terrorism that seek weapons of mass destruction. Iran has rejected the characterization.