President Bush said Wednesday the United States has not yet reached agreement with the Czech Republic to allow installation of a U.S. missile-defense radar there, but that the two sides are close.

A radar facility in the Czech Republic is part of a plan that also calls for placing 10 missile interceptors in Poland. The Bush administration says the program is necessary to allow the United States and Europe to deal with a potential threat from Iran or other potential foes.

Russia is fiercely opposed to the prospect of U.S. military installations plan.

There had been some expectation that Bush and Czech Prime Minister Mirek Topolanek would sign an agreement on the issue during their White House meetings Wednesday. But Bush said after their talks that they merely had a good discussion and are now "down to three words" to complete an agreement.

Bush declined to reveal their remaining differences, but Topolanek said it is the Czech demand for the "strictest possible standards" to apply to any environmental matters related to the future U.S. military presence in his country.

"But that's just a technical matter, which is going to be resolved very soon," the Czech leader said.

White House press secretary Dana Perino would not say whether the U.S. opposes requiring the strictest environmental standards. "Obviously we are going to adhere to environmental standards wherever we go and whatever activities we are doing, both here in the United States and around the world," she said.

Bush said the negotiations are complicated, amounting to essentially devising a status of forces agreement with the Czech Republic to govern how U.S. personnel conduct themselves and under what terms. "These are all very legitimate questions that the prime minister is asking, and the same questions are being asked in Poland," he said.

"There is a will to get it done," Bush said. "These aren't easy agreements to put in place."

The leaders discussed Russia's opposition, and Bush said he was encouraged to hear Topolanek say that it is the Czech government, not Moscow, that will determine what happens on its soil. "He made it clear to me that the Czech Republic will be making decisions about who gets to come into their country."

Russia has threatened to target any future base in Poland with its missiles, which has caused deep anxiety in Warsaw since talks began a year ago. Though the Czechs have been generally receptive to the idea of installing missile-tracking radar southwest of Prague, Poland has been more reticent since a new government took office there in November.

Any deal Topolanek signed would have to be ratified by the Czech parliament.

"Russia is not a threat to peace," Bush said. "This is a system to deal with threats that will be evolving in the 21st century."

Also topping the Oval Office meeting agenda was an agreement reached Tuesday between the United States and the Czech Republic to move toward letting Czech citizens travel to the United States without visas, perhaps as early as September.

Bush said the new memorandum of understanding is not the final chapter, but that the Czech Republic is now "ahead of the line of anybody else when it comes to a visa waiver program."

"We still have more work to do," he said. "But I'm confident we can get it done."

"The negotiations have been really tough," Topolanek said, while describing the developments as "a true breakthrough moment" and "a great achievement" for his country's push to integrate with the West since the end of Soviet domination of Eastern Europe.

The United States passed a law last year aimed at expanding its visa-waiver program for citizens from some countries, but the program has caused frustration in Europe because some countries were left out.

The document outlines what the Czech government will have to do to conclude a deal, including stepping up information-sharing with biographic and biometric data on Czech visitors to the United States and ensuring the tracking of lost or stolen passports.

Topolanek said his country is aware of the "risks and dangers" from terrorism and promised Bush that he would guarantee higher security over travelers.