Mr. Medvedev responded by telling Mr. Obama he would “transmit this information to Vladimir” — current Russian President Vladimir Putin.
The comments sparked widespread concern among House Republicans, including Speaker John A. Boehner of Ohio and Armed Services Committee Chairman Howard P. “Buck” McKeon of California, who sought answers from the White House on the issue but to date have received none.
The issue of a president making a secret assurance to a foreign leader is unprecedented. Yet no news outlet or reporter who has interviewed the president since the March comments has asked him what he meant by the secret promise of flexibility.
As guaranteed by the president, missile-defense talks with Russia have been on hold and are expected to resume in the coming weeks.
Future flexibility with Russia was outlined recently by Frank A. Rose, deputy assistant secretary of state for arms control, verification and compliance. He said in a September speech in Berlin that despite differences with Russia, missile-defense cooperation remains a presidential priority.
Mr. Rose said the administration “cannot agree” with Russian proposals to create “sectoral” or “joint” missile defenses because they that would undermine NATO defenses.
“Furthermore, we cannot accept Russia’s demand for legally binding guarantees that our missile defenses will not threaten Russia’s strategic deterrent,” he said.
“Russia’s demand that such guarantees include a set of ‘military-technical criteria’ would create limitations on our ability to develop and deploy future missile-defense systems against the evolving ballistic-missile threats presented by Iran and North Korea.”
He insisted the United States would not place “artificial limits on our ability to defend ourselves, our allies, and our partners.”
However, the administration is set to agree to a “political framework for cooperation” that would include a statement that U.S. and NATO missile defenses are not “oriented toward Russia,” he stated.
Mr. Rose said one area of growing cooperation was allowing Russia to join a regional missile-defense exercise with NATO held earlier this year.
Other “ideas and approaches for transparency” were made to Moscow as part of confidence-building measures he did not specify.
Congress recently passed legislation blocking the administration from sharing classified missile-defense data with the Russians.
U.S. intelligence agencies are closely studying the new military lineup at the top ranks of the People’s Liberation Army.