By a vote of 71-26, the U.S. Senate Dec. 22 ratified the U.S.-Russia New START treaty setting new limits on the two countries’ long-range nuclear weapons arsenals, marking a significant foreign policy achievement for the Obama administration during the lame-duck Congressional session.

The two-thirds majority needed to pass the treaty seemed assured after 11 Republican senators earlier defied their top leadership and voted with Democrats to end debate on the treaty.

Though Senate Minority Leader Mitch McConnell, R-Ky., and the Minority Whip, Arizona’s Jon Kyl, had pledged to oppose the treaty, another top Republican leader, Tennessee’s Lamar Alexander, said he would back the pact.

Among New START’s backers were the Foreign Relations Committee’s ranking Republican, Indiana Sen. Richard Lugar, and two other Republican committee members who had earlier voted to send the treaty to the Senate floor.

New START was signed by Obama and Russian President Dmitry Medvedev last April. It requires each side to limit deployed long-range nuclear warheads to 1,550 – about a one-third reduction from the previous treaty. Deployed nuclear-capable submarines, long-range missiles and heavy bombers are capped at 700, with 100 more in reserve. It also reinstitutes on-site inspections by each country of the other’s arsenal – a provision that lapsed when the previous treaty expired over a year ago.

Republicans overwhelmingly backed earlier arms agreements with Russia, and before that, with the Soviet Union. But they were seriously split this time. Some, including McConnell and Kyl, seemed determined to make the treaty a pawn in their struggle to defeat any Obama administration initiative, even though most past and present members of the U.S. military and foreign policy establishment supported the pact.

Republicans also held the treaty hostage to their demands for huge expenditures to modernize the U.S. nuclear missile facilities and for a strong administration commitment to development of missile defense systems. Many analysts regard modernization as unnecessary to maintain the current strength of the U.S. arsenal, and missile defense as potentially leading to a new arms race.

During the debate, Foreign Relations Committee chair Sen. John Kerry, D-Mass., successfully held off several efforts to amend the treaty itself, which would have meant reopening negotiations with Russia.

But the Senate did approve several amendments to the resolution of ratification. The resolution doesn’t affect the treaty itself or require its renegotiation. One amendment mandates the president to certify to Congress that he supports a broad range of missile defenses. Another requires Obama to promise to negotiate with Russia on tactical nuclear arms. A third instructs him to modernize delivery vehicles for the long-range nukes.

In the days before the treaty’s passage, President Obama had sent Senate Republicans letters confirming the administration’s commitment to modernization, and to missile defense.

Russian Foreign Minister Sergey Lavrov had earlier warned that the treaty “cannot be opened up and become the subject of new negotiations.”

And on Wednesday, Moscow News quoted Russia’s ambassador to NATO, Dmitry Rogozin, as saying, “In essence, the U.S. Senate will confirm both financially and politically that the global missile defense system will not face any limitations. As a former parliamentarian, I suspect that this could result in similar amendments from the Russian side.”

Image: Ratification of the New START Treaty is a step towards Obama’s goal of a nuclear weapons-free world, as expressed in his speech in Prague, Czech Republic, April 5, 2009. (Official White House Photo by Pete Souza)