The U.S. Senate on Wednesday approved a new nuclear arms-reduction treaty with Russia, the broadest such pact between the former Cold War foes in nearly two decades.

The Senate ratified the New Strategic Arms Reduction Treaty, known as New START, by a vote of 71 to 26, easily clearing the threshold of two-thirds of senators present as required by the Constitution for treaty ratification.

The final vote came after Senate Democrats accepted two amendments designed to placate Republicans who had qualms about the treaty. The amendments, which passed on voice votes with bipartisan support, emphasized the administration's commitment to a limited missile-defense program and to continued funding to modernize the aging U.S. nuclear weapons complex.

The amendments were to the resolution of ratification accompanying the treaty, a nonbinding statement that codifies the Senate's understanding of the pact but does not directly affect its language. Republican efforts to alter the treaty language were defeated, with supporters of the pact arguing that such changes would have forced new negotiations with Moscow and effectively killed the treaty.

Thirteen Republicans joined all of the Senate's Democrats in voting for ratification, helping to exceed the 67 votes required. Three senators - all Republicans - were not present.

In a floor speech shortly before the ratification vote, Sen. John F. Kerry (D-Mass.), the Foreign Relations Committee chairman who shepherded the treaty through the Senate, implored senators to put politics aside and take a broad view. "This is one of those rare times in the United States Senate . . . when we have it in our power to safeguard or endanger human life on this planet," he said. "More than any other, this issue should transcend politics. . . . More than at almost any other time, the people of the world are watching us because they rely on our leadership."

Kerry also chided Republicans who had argued against taking up New START ratification so close to Christmas, thus delaying their departures for the holidays. "The question is not whether we get out of here for a holiday; the question is whether we move the world a little more out of the dark shadow of nuclear nightmare," he said.

Kerry said after the vote: "The winners are not defined by party or ideology. The winners are the American people, who are safer with fewer Russian missiles aimed at them." He said the treaty's impact "will echo around the world," showing that the United States remains determined to work with Russia and other countries to reduce the global threat from nuclear weapons.

"With this treaty, we send a message to Iran and North Korea that the international community remains united to restrain the nuclear ambitions of countries that operate outside the law," Kerry said.

New START cleared a key hurdle in the Senate on Tuesday, advancing to a final vote with a margin that appeared to guarantee ratification and a major foreign-policy victory for President Obama. Senators voted 67 to 28 to invoke "cloture" to limit further debate and move to the ratification vote, with 11 Republicans joining all 56 Democrats present in the chamber.

The stakes were high: Defeat of the pact would have severely damaged Obama's global standing, hampering his ability to negotiate other treaties, and would have dealt a major setback to the president's "reset" of relations with Russia.

"It's one of those things in life where failing to get it would be more important than actually what you get with it," said George Perkovich, a scholar on nuclear nonproliferation at the Carnegie Endowment for International Peace.