MOSCOW - Russians are mystified. They can't quite believe the U.S. Senate might fail to ratify the nuclear arms treaty, and they see no good from such an outcome.

The list of possible harmful effects they cite encompasses a minefield of global concerns: no more cooperation on Iran, a setback for progressive tendencies in Russia, new hurdles for Russian membership in the World Trade Organization, a terrible example for nuclear countries such as China and India, dim prospects for better NATO relations. And to top it off, the United States and its president would look ridiculous.

"The result will by no means be nuclear catastrophe," said Igor S. Ivanov, a former foreign minister, searching for a bright note, "but there will undoubtedly be negative results, and not just for U.S.-Russian relations."

If the two great nuclear powers cannot come to terms, he said, nonproliferation efforts worldwide would be seriously damaged. And for what? "It's a well thought-out and balanced document," good for both countries' security, Ivanov said Thursday.

Sergei M. Rogov, director of the Institute for U.S. and Canadian Studies, said he had difficulty believing Republicans are serious about killing the New START treaty, even though Republican Sen. Jon Kyl of Arizona said Tuesday there was not enough time to consider it in the lame-duck session. A vote next year makes ratification harder because a loss of Democratic seats means 14 Republican votes will be required for passage rather than nine now.

"In arms control, Russian and American cooperation is crucial," Rogov said. "I really don't think Republicans want to kill arms control."

Also at risk is the administration's "reset" of ties with Russia and impetus for the modernization encouraged by President Dmitry Medvedev, who signed the treaty with President Obama in April. Russia intends to ratify it at the same time as the United States.

"This administration deserves some credit for the improvement in U.S.-Russian relations. One of the casualties of a failure to ratify would obviously be that relationship," said Richard Haass, president of the Council on Foreign Relations, who held senior foreign-policy positions in both Bush administrations. "It would reinforce the most nationalist tendencies in Russia."

Russian WTO membership is coupled with repeal of the Cold War-era Jackson-Vanik amendment. Anti-Russian sentiment could doom the removal of those trade sanctions, Rogov said, especially with a Republican-majority House.

Russia would not backtrack on its refusal to sell Iran missiles, he added, but additional sanctions would not be supported. Nuclear countries such as China and India would have little reason to limit their own arsenals. Then there's NATO.

"It would be pretty difficult to expect true cooperation between Russia and NATO," he said.

Cooperation over Afghanistan would likely go unscathed because Russia has dramatically changed its views since 2008, when it offered Kyrgyzstan a $480 million loan if it would close down the American base at Manas, used to send U.S. troops into the war zone. Now Russia sees cooperation in Afghanistan as in its interests, said Alexander Goltz, a military affairs analyst.

Not so with Iran. "That's totally different," Goltz said. "From the beginning, Russia has looked at Iran as a good card to play with the U.S. Cooperation on Iran can be the real victim of a failure to ratify the treaty."

And think of how the United States - and particularly Obama - would look, Rogov said.

"The fact that America can't deliver on its promises would harm its standing around the world," he said. "And if START is not ratified, the [2009] Nobel Peace Prize would look very funny indeed."

Staff writer Mary Beth Sheridan in Washington contributed to this report.