PRAGUE, Czech Republic — The United States and leaders of the Czech Republic agreed Tuesday to place a radar system in this former Soviet satellite that would warn of long-range missiles coming to Europe from the Middle East.

Secretary of State Condoleezza Rice turned old Cold War rhetoric away from Moscow and toward Tehran as she signed the first solid treaty in what have been difficult negotiations.

Iran looms as an ever-larger threat and the next U.S. president is unlikely to walk away from the missile defense system the Bush administration is trying to establish in Eastern Europe, Rice said.

The proposed U.S. missile defense system calls for a tracking radar in the Czech Republic and 10 interceptor missiles in Poland. Moscow has threatened to aim its own missiles at any eventual base in Poland or the Czech Republic.

Shortly after the treaty was signed, Russia's Foreign Ministry said Moscow would be forced to initiate a military response if the deal goes ahead. If the agreement is ratified, "we will be forced to react not with diplomatic, but with military-technical methods," the Foreign Ministry statement said.

In February, then-President Vladimir Putin said that if the plan advances, Russia could aim missiles toward prospective missile defense sites and deploy missiles in the Baltic Sea region, which borders Poland.