Lack of outright Senate opposition, so far, to the new arms reduction treaty that President Barack Obama is to sign with Russia this week does not guarantee quick approval — or even that approval will happen at all.

Supporters, though, are confident that the treaty will ultimately win approval in the Senate where Obama’s Democrats have the majority, but not the required 67 — or two-thirds– vote.

“I’m pretty confident that if we can get this treaty to a final vote, not only will the treaty pass, but it will pass with a very large majority,” said John Isaacs, Executive Director of the Center for Arms Control and Non-Proliferation.

Obama and Russian President Dmitry Medvedev meet in Prague on Thursday to sign the successor to the 1991 Strategic Arms Reduction Treaty. The new START commits the ex-Cold War foes to cut arsenals of deployed nuclear warheads by about 30 percent.

The White House hopes that by the end of 2010, the Senate as well as Russia’s parliament, the Duma, will have approved the deal. Senate committee hearings could begin this spring, as soon as the treaty and annexes are sent to Capitol Hill. No action is required in the House of Representatives.

Analysts say potential obstacles to the Senate’s consent lie not so much in what is in the new treaty, but concerns that some Republicans have raised about related matters: U.S. missile defense programs and the modernization of the U.S. nuclear arsenal.

U.S. politics and procedural rules could also delay Senate action and indirectly, that of Russia’s Duma. Russian officials say they want to “synchronize” ratification, suggesting they may not be willing to vote until the Senate does.

But Senate Republicans soured by the recent healthcare battle with Obama may be in no rush to hand him a foreign policy victory ahead of November congressional elections.

“There is a danger that it (the new START) will have difficulty overcoming the intense partisan obstructionism in that body,” analysts Max Bergmann and Samuel Charap of the Center for American Progress wrote this week.

ARGUMENTS FOR APPROVAL

On the merits, there has been little criticism of the new START so far. Many lawmakers in both U.S. political parties favor nuclear arms reductions, as well as keeping some level of cooperation going with the Russians.

Many are also likely to think that some means of verifying Russia’s nuclear arsenal is better than none. The old START treaty expired last December, although both sides pledged to uphold the spirit of the deal while seeking a replacement.

If things do get tricky in the Senate debate, “it’s because the debate becomes broader, rather than just the narrow debate about the provisions of the treaty,” said Tom Donnelly, defense analyst at the American Enterprise Institute.

Republicans are looking for evidence that Obama will keep the remaining U.S. arsenal up-to-date, he said.

U.S. missile defense programs are not limited by the treaty, but they are another potential source of trouble in the ratification process. Russian Foreign Minister Sergei Lavrov says Moscow will withdraw from the new START treaty if U.S. missile defense threatens Russia, although he suggested this was unlikely to happen in the near future.

Stephen Rademaker, a former head of the State Department’s arms control bureau, said some U.S. senators might wonder why they should vote for the treaty if the Russians intend to use it as leverage to stop missile defense policies that Obama already has declared.

“Is there an intention on both sides to live with this treaty, or are the Russians essentially coming to this wedding declaring that they want to get married but they don’t intend to live in holy matrimony?” Rademaker asked during a forum at the Heritage Foundation in Washington this week.

But Ambassador Linton Brooks, who negotiated the first START treaty under former President George H.W. Bush, noted that Russian statements about missile defense may be aimed at Russian audiences.

“It would be tragic if we allowed Russian statements made for domestic purposes to derail it (new START),” he said.