A Republican U.S. senator said Tuesday he will try to block a U.S.-Russia civilian nuclear power deal if President Bush sends it to Congress, because he fears it could undermine efforts to prevent nuclear proliferation in Iran.

Sen. Norm Coleman said he is teaming with Democratic Sen. Evan Bayh in circulating a letter that will urge Bush not to send the pact to Congress.

Under the deal signed Tuesday, the United States would get access to Russian state-of-the art nuclear technology. The pact would help Russia establish an international nuclear fuel storage facility by importing and storing spent fuel. The United States controls most of the world's nuclear fuel by far.

"I am very disappointed by the administration's insistence on moving forward to sign a nuclear cooperation arrangement with the Russians," Coleman said in a telephone interview. "Particularly at a time when Russia's actively undermining our foreign policy on various fronts, most importantly with respect to Iran."

In a statement, Bayh said: "U.S.-Russian nuclear cooperation is important, but stopping Iran from gaining the capacity to make nuclear weapons is an even higher priority. Russia is not doing all it can to curb Tehran's nuclear ambitions, and we need to use all tools at our disposal to get more cooperation from Moscow."

Coleman and Bayh say Russia's exports of nuclear fuel to Iran's Bushehr nuclear power plant and opposition to United Nations sanctions against Iran make the new deal suspect. In the letter, provided to The Associated Press, the senators say the deal "would pave the way for the increased commercialization of Russia's nuclear energy sector and could be construed as U.S. approval of its proliferation activities in Iran."

The Bush administration now views Russia as a partner in the effort to persuade Iran to abandon any nuclear weapons ambitions it may have. A State Department official said the United States did not view Russia's assistance to Iran's Bushehr nuclear power plant as a reason to not sign the new deal.

"In fact, the president has made clear his support for Russia's supply of nuclear fuel to Bushehr because it demonstrates that Iran does not need to possess the complete nuclear fuel cycle with its proliferation risks to take advantage of the peaceful uses of nuclear energy," said the official, who asked not to be identified because he was not authorized to speak on the record.

To get the deal in place, Bush must send it to Congress. It would become effective unless Congress should pass legislation within 90 days to block it.

A bill pending in the Senate would block a U.S.-Russia nuclear deal unless Russia has stopped cooperating with Iran's nuclear or advanced conventional and missile program or Iran has stopped enriching uranium. That legislation, sponsored by Republican Gordon Smith, has 70 co-sponsors, but Coleman said it is no sure bet that it would be passed in time to block the deal signed Tuesday.

"Even if you have the votes, it doesn't mean you'll have time to take it up and debate it," he said. "There's no guarantee that leadership will schedule a vote."

"There is a great deal of concern on the part of many members of Congress," Coleman added. "I disagree with the president; I think it's bad policy."

He said that Bush could use congressional opposition as leverage in extracting conditions from the Russians for the deal. "At a minimum," he said, "they have to stop with any advanced conventional weapon assistance to the Iranians."