An unusual split has opened between conservative Republicans and the American military leadership over the U.S.-Russia nuclear treaty, with current and former generals urging swift passage but politicians expressing far more skepticism.

Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, has called the New Strategic Arms Reduction Treaty (New START) "essential to our future security." Retired generals have been so concerned about getting it ratified that some have traveled around the country promoting it.

Seven of eight former commanders of U.S. nuclear forces have urged the Senate to approve the treaty.

But five Republicans on the Senate Foreign Relations Committee said in a recent report that New START was "a bad deal." They added that U.S. military leaders had made assumptions about the pact - including that Russia will honor it - that are "optimistic in the extreme."

Meanwhile, the conservative Heritage Foundation's grass-roots lobbying arm is targeting Republican senators with mailings warning that the treaty "benefits Russia's interests, not ours."

Retired Lt. Gen. Dirk Jameson, the former deputy commander of U.S. nuclear forces, said Friday that it was "quite puzzling to me why all of this support [for New START] . . . is ignored. I don't know what that says about the trust that people have and the confidence they have in our military."

The New START treaty would reduce the two nuclear giants' stockpiles of long-range, deployed weapons by as much as 30 percent, leaving each country with about 1,550 warheads. President Obama said Thursday that he had "no higher national security priority" during the lame-duck session than having it ratified.

Winning approval could be tougher next year, when Republicans will have five more votes in the Senate.

For current and former senior U.S. military officials, the treaty is valuable because it allows the continuation of a dialogue with a country that still has enough weapons to wipe America off the map.

"If you've had experience with this stuff, and a sense of where we've been, how far we've come . . . this is an absolute no-brainer," said retired Adm. William J. "Fox" Fallon, who was head of Central Command and Pacific Command.

Military leaders say the treaty will allow the two countries to resume inspections of each other's stockpiles, which make up 95 percent of the world's nuclear weapons. Such visits lapsed when the first START treaty expired last year.

Without such inspections, U.S. military leaders would have less insight into Russia's arsenal and might have to work off worst-case scenarios, and could consider increasing their own stockpile, officials say.