WASHINGTON — A senior Republican senator on Tuesday downplayed prospects for a vote this year on a new nuclear-arms accord with Russia, the centerpiece of an Obama administration effort to “reset” relations with Moscow that has the support of U.S. military commanders and national security experts of both parties.

Sen. Jon Kyl of Arizona, the second-highest-ranking Republican senator and the GOP’s leading voice on nuclear-weapons issues, said the lame-duck Senate had too many other issues before it, leaving insufficient time to consider the New START treaty.

“When (Senate) Majority Leader Harry Reid asked me if I thought the treaty could be considered in the lame-duck session, I replied I did not think so, given the combination of other work Congress must do and the complex and unresolved issues related to START and modernization,” Kyl said in a statement.

The statement comes as the Obama administration tries to win a vote by meeting Kyl’s demand for more funds to modernize the facilities that maintain U.S. nuclear warheads.

Kyl appeared to reject the offer, but at the same time left an opening for a deal.

Sen. John Kerry, D-Mass, the chairman of the Senate Foreign Relations Committee, said he thought that a vote could still be held.

“I talked with Sen. Kyl today, and I do not believe the door is closed to considering New START during the lame-duck session,” Kerry said. “Ratifying New START is not a political choice; it’s a national security imperative.”

Sen. James Inhofe, R-Okla., a conservative member of the Senate Armed Services Committee and the Foreign Relations Committee, went beyond Kyl, saying, “It’s time to start over with START.”

“Historically, no major nuclear arms control treaty has ever been taken up in a lame-duck (Senate), and, as I have pointed out repeatedly, the one-sided nature of the hearings before the Senate has not begun to adequately examine this treaty’s ramifications,” Inhofe said.

Kyl, Inhofe and other conservative lawmakers contend that the accord would constrain the development of U.S. anti-missile defenses, an assertion denied by the Obama administration, the Joint Chiefs of Staff and other top U.S. commanders, who have called for its swift approval.

President Obama and Russian President Dmitri Medvedev signed the treaty in April. U.S. officials viewed it as the main pillar of an initiative to “reset” relations with Moscow that had sunk under former President George W. Bush to their chilliest level since the Cold War ended in 1991.