OSLO, April 26 — Brusquely dismissing protests by Russian officials, Secretary of State Condoleezza Rice said here on Thursday that a missile-defense system the United States plans to install in Poland and the Czech Republic would pose no danger to the security of Russia.

“The idea that somehow 10 interceptors and a few radars in Eastern Europe are going to threaten the Soviet strategic deterrent is purely ludicrous, and everybody knows it,” Ms. Rice said before a meeting of NATO foreign ministers expected to focus on the missile-defense dispute.

“The Russians have thousands of warheads,” Ms. Rice said. “The idea that you can somehow stop the Soviet strategic nuclear deterrent with a few interceptors just doesn’t make sense.”

Still, Ms. Rice said the United States would continue discussing the system with Russian officials, in an effort to “demystify” it. She planned to meet the foreign minister, Sergei Lavrov, later on Thursday.