WASHINGTON -- President Barack Obama's administration said Tuesday that it had not yet decided how far to implement former President George W. Bush's plan for a missile defense system in Central Europe, which is strongly opposed by Russia.

"No final decisions have been made regarding missile defense in Europe," Deputy Defense Secretary William Lynn said in remarks that drew expressions of surprise from members of the Senate Armed Services Committee.

Lynn described the proposal to install 10 two-stage interceptor missiles in Poland and a radar station in the Czech Republic as only "one option" or "one alternative" under review.

He said the United States also was exploring expanded missile defense cooperation with Russia as a means of countering a perceived threat from Iranian ballistic missiles.

"The United States will work to identify new areas where our two countries could advance our missile defense cooperation," Lynn testified. "For example, there are Russian radars near Iran that would provide helpful early warning detection in the case of an Iranian ballistic missile launch."

He said the possible use of the radars -- in southern Russian and Azerbaijan -- would be discussed when Obama visits Moscow from July 6 to 8, where he hopes to build on calls from both capitals to reset relations.

Lynn said the United States was committed to an effective defense against "rogue" threats, including North Korea and, "if it continues down its current path, Iran."

Missile defense cooperation with Russia has been a consistent goal since the 1990s, he said.

On April 5, Obama said the United States planned to go forward with a missile defense system that is "cost-effective and proven" as long as a threat from Iran persists.

"If the Iranian threat is eliminated, we will have a stronger basis for security, and the driving force for missile defense construction in Europe at this time will be removed," he said in a major speech on the subject in Prague.

Committee member Senator Jeff Sessions commented that U.S. hesitation over the missile plan would "undermine the Poles' and the Czechs' willingness" to host the installations.

The parliaments of Poland and the Czech Republic have not yet ratified the proposed installations on their soil. Poland is expecting to receive Patriot anti-missile batteries as part of the deal.