The Obama administration is leaving open the possibility of giving Moscow certain secret data on US interceptor missiles due to help protect Europe from any Iranian missile strike.

A deal is being sought by Washington that could include classified data exchange because it is in the US interest to enlist Russia and its radar stations in the missile-defense effort, a Pentagon spokeswoman said Tuesday in written replies to Reuters.

No decision has been made yet on whether the United States would offer data about the interceptors' "velocity at burnout," or VBO, said Air Force Lieutenant Colonel April Cunningham, the spokeswoman, but it is not being ruled out.

VBO is at the heart of what Russia wants as the price for its cooperation, said Riki Ellison, head of the private Missile Defense Advocacy Alliance, who has close ties to missile defense and military officials.

VBO tells how fast an interceptor is going when its rocket-booster motor fuel is spent and the motor burns out.

With VBO and certain other technical data, Moscow could more readily develop countermeasures and strategies to defeat the system and transfer the information to others, Ellison said.

Ellen Tauscher, the administration's special envoy for strategic stability and missile defense, held talks in Moscow Tuesday with Russian Deputy Foreign Minister Sergei Ryabkov, including on missile defense, a State Department spokesman said.

The Defense Department, in its response to Reuters, ruled out giving Russia information on either "telemetry" or US "hit-to-kill" technology.

Telemetry involves the automatic transmission and measurement of data from remote sources to monitor a missile flight. Hit-to-kill is the way in which modern US interceptors, such as Raytheon Co's (RTN.N) Standard Missile-3, destroy targets by slamming into them.

The department emphasized the Obama administration was following in the footsteps of the George W. Bush administration in seeking missile defense cooperation with Moscow, a process formally begun in 2004.

In keeping open the possibility of sharing VBO information with Moscow, Obama is at odds with Republicans in Congress who have said they will seek to legislate a prohibition on such data-sharing.

Republican Rep. Mike Turner, chairman of the House of Representatives' Armed Services subcommittee on strategic forces, faulted the administration for what he described as "caving" to Russian concerns at the expense of US interests.

"That is why it is important Congress insist on protecting our classified missile defense information, and our right to deploy missile defenses without concern for Russia's posturing," he said in a statement Tuesday to Reuters.

The sharing of such data might help salve Russian concerns about the layered shield being built in Europe by the United States and its NATO allies, chiefly to fend off the perceived threat from Iranian missiles.

Moscow fears the bulwark could grow strong enough over time to undermine its nuclear deterrent force. It has threatened to deploy missiles to overcome the shield and potentially target missile defense installations such as those planned in NATO members Poland and Romania.

The Defense Department, in its reply to Reuters, said the sharing of classified US data is subject to an interagency group known as the National Disclosure Policy Committee, which evaluates requests for dealing with other governments.

Bradley Roberts, a deputy assistant secretary of defense, told Turner's committee last week the United States had been making "no progress" toward persuading Russia to drop its opposition to the shield despite its willingness to consider sharing certain classified data.