MOSCOW - Prime Minister Vladimir V. Putin said yesterday that Russia wanted the United States to share detailed data about its planned missile shield under a new arms-control treaty, signaling potential new difficulties in the negotiations between Moscow and Washington.

Putin's televised remarks set a defiant tone as negotiators try to work out a successor to the 1991 Strategic Arms Reduction Treaty that expired Dec. 5. The two countries had hoped to reach a deal before the end of the year, but problems persist.

Putin also said Russia would build new weapons to offset the U.S. missile-defense system.

The State Department rejected Putin's call, saying the START successor treaty would deal only with strategic offensive arms.

"While the United States has long agreed that there is a relationship between missile offense and defense, we believe the START follow-on agreement is not the appropriate vehicle for addressing it," spokesman Ian Kelly said in Washington.

"We have agreed to continue to discuss the topic of missile defense with Russia in a separate venue," he said.

Putin's comments showed that the former Russian president was still shaping Russian foreign policy, which under the constitution should be set by his successor, Dmitry A. Medvedev.

He said that the arms-control talks were proceeding in a positive way and added that Medvedev and President Obama would eventually decide whether to strike an arms deal.

But Putin warned that a missile-defense system would give the United States an edge and could erode the deterrent value of Russia's nuclear forces.

"The problem is that our American partners are developing missile defenses, and we are not," Putin said.

"There could be a danger that having created an umbrella against offensive strike systems, our partners may come to feel completely safe. After the balance is broken, they will do whatever they want and grow more aggressive."

Obama removed a major irritant in relations earlier this year by scrapping Bush administration plans to place interceptor missiles in Poland and a radar in the Czech Republic - deployments that Russia treated as a threat.

The Kremlin has praised Obama for the decision, but Russian officials have also said they want to know more about the sea- and land-based systems the United States plans to put in place instead.