Russia's top diplomat accused the United States of launching a new arms race as the two nations traded barbs Wednesday over U.S. plans to erect a missile defense system in countries formerly under Moscow's influence.

Russian Foreign Minister Sergey Lavrov complained that the U.S. rationale for the shield is thin and suggested that U.S. assurances to Russia amount to a brush-off.

"All they are saying is, 'Don't worry it's not aimed at you," Lavrov said. He called the plan a threat to Russia and added, "the arms race is starting again."

Secretary of State Condoleezza Rice said the United States has repeatedly explained its plan to Russia in considerable detail, and stands ready to discuss the matter further. She tartly noted that Russian President Vladimir Putin himself had said Russia's own strategic defenses could easily overpower the U.S. system.

"We quite agree," she said.

Lavrov made a dark joke in response.

"I hope that nobody has to actually prove that Condi is right about that," Lavrov said.

On Tuesday, Russia tested a new multiple-warhead, intercontinental ballistic missile, and Putin warned that the planned U.S. missile shield would turn Europe into a "powder keg."

President Bush, Rice and Secretary of Defense Richard Gates have all tried to reassure the Russians about the program, and U.S. officilas suggest that Russia is using the issue to score political points.

Speaking to reporters ahead of her trip to Europe, Rice poo-pooed Russian complaints.

"The idea that this somehow would degrade Russia's strategic nuclear deterrent is just ludicrous, and the Russians know it's ludicrous," Rice said. "There isn't any military person who can imagine this system with a few interceptors and a few sensors and a few radars able to intercept the Russian deterrent."

Lavrov took issue with that Wednesday.

"For us this is not ludicrous at all, and I hope our American partners will respect our analysis which we have presented to them in a very professional and detailed way," he said.

U.S. officials say the deployment of 10 interceptor missiles in Poland and a radar system in the Czech Republic would protect Russia and the rest of Europe from potential attack by Iran, North Korea or other nations.

The European sites are part of a larger shield that the Bush administration envisions for Europe and North America. Besides opposition from Russia, the program is hitting a roadblock at home.

The administration is facing the prospect of a sharp cut by the Democratic-contolled Congress in its request for $310 million to begin developing the system. Last week the Senate Armed Service Committee cut $85 million from the administration request.

The Kremlin says the system threatens the strategic balance of forces in Europe by weakening Russia's ability to retaliate against an offensive strike.

"We are still convinced that the only target of that shield would be not the purely hypothetical threat that might come from Iran or some other remote state, but the only real target will be our country," Kremlin spokesman Dmitry Peskov told The Associated Press on Tuesday.

Rice, Lavrov and other diplomats were gathered for a working session ahead of next month's Group of Eight summit of leading industrial nations. That meeting will be closely watched for signs of a rift between Bush and Putin.

The two presidents will also meet July 1 and 2 in Kennebunkport, Maine, administration officials said Wednesday. Bush's father, former President George H.W. Bush, has an oceanfront compound in Kennebunkport.

Putin, once celebrated by fellow members of the elite international club, has in recent years found himself quarreling with other members, especially the United States, and has been openly disgruntled with the G-8's brand of global politics.

Recent rhetoric between Washington and Moscow has been marked by rancor and distrust, with the missile defense issue a leading example.

Putin delivered a May 9 speech in Red Square that seemed to compare Bush's foreign policy to that of the Third Reich, while in February he accused the U.S. of "an almost uncontained hyper use of force that is plunging the world into an abyss of permanent conflicts."

Bush, meanwhile, has talked of mutual suspicions between the two nations.