"This is not an issue that can afford to be postponed," Clinton said after meeting lawmakers. "The administration ... will do whatever it takes to reach out, to answer questions, to have discussions."

A day after a key Senate Republican expressed doubts about President Barack Obama's drive to ratify the accord before January, White House spokesman Robert Gibbs sought to dispel the notion that the treaty had been dealt a serious blow.

Gibbs said the administration was confident the Senate would take up the strategic arms treaty before Congress ends its term this year.

Analysts say the START debate reflects growing polarization in Congress over public policy and U.S. national security.

Obama and Russian President Dmitry Medvedev signed the New START treaty in April to replace the previous START accord, which expired last December. The new agreement commits the former Cold War foes to cut deployed nuclear weapons by about 30 percent, to no more than 1,550, within seven years.

The accord is seen as one of Obama's top foreign policy accomplishments, a part of his effort to improve relations with Russia and his drive against nuclear proliferation. He promised Medvedev on Sunday that ratification during the final weeks of the year was a priority for his administration.