WASHINGTON  Vexed and cornered, Republican opponents of the advancing effort to allow gay men and lesbians to serve openly in the military pulled out a final card Friday, suggesting that the future of an arms treaty with Russia was endangered by Democratic efforts to repeal “don’t ask don’t tell” at the end of the lame-duck session.

“It poisons the well,” said Senator Bob Corker, Republican of Tennessee, on the floor of the Senate during debate on the New Start treaty. Mr. Coker said he did not think “the future of the Start treaty over the next several days is going to be successful” if Senator Harry Reid, the majority leader, continued with his plans to pursue the repeal, as well as an immigration bill.

Other Republican senators echoed the view.

Mr. Reid announced Thursday that the Senate would begin voting Saturday on a measure to repeal the Clinton-era military policy that prohibits gay, lesbian and bisexual members of the military from serving openly. The Senate will also take up an immigration bill that would allow young people who were illegally brought into the country to earn legal status through education or military service. Its passage, which is considered unlikely, would fulfill a campaign promise that Mr. Reid made to Hispanic voters.

The repeal measure, once tucked into a broader military bill that failed to win approval, was returned to the Senate this week after being passed by the House, and appears to have just enough Republican votes to pass.