Washington ? President Barack Obama predicted on Thursday that enough Republicans will support his arms control treaty with Russia to win Senate approval by the end of the year.

History is on his side, even if numbers in the Senate are not. He will need 67 votes in a chamber where Democrats control 59 votes and in a sour political climate that could tempt Republicans to set aside the nonpartisan deference often given to national security treaties.

President Barack Obama, with Russian President Dmitry Medvedev, left, and Czech Republic President Vaclav Klaus, share a toast Thursday in Prague after signing the nuclear arms treaty. Obama is hoping for Senate approval of the deal by year’s end.

“There is a strong history of bipartisanship when it comes to the evaluation of international treaties, particularly arms control treaties,” Obama said in Prague, where he signed the new strategic nuclear weapons pact with Russian President Dmitry Medvedev.

Republicans were expected to swing behind the treaty if Obama can promise it won’t undercut the nation’s ability to set up missile defenses to protect against an attack from Iran or North Korea.

They also want assurances that the agreement will preserve what’s known as the “nuclear triad” — the nation’s ability to deliver nuclear weapons from the air, land and sea.

The nuclear weapons cuts Obama and Medvedev signed on Thursday would shrink the Cold War superpowers’ arsenals to the lowest point since the frightening arms race of the 1960s. But they won’t touch the “loose nukes” and suitcase bombs seen as the real menace in today’s age of terrorism.