Lawmakers worry that a U.S.-Russian deal on civil nuclear power could undermine efforts to rein in Iran's nuclear program.

To a Bush administration arms control expert, it is a "solid agreement" that can help the United States tackle 21st century challenges such as growing energy demands, nuclear nonproliferation and possible nuclear terrorism.

Undersecretary of State John Rood faced opposition from both Democrats and Republicans on the House Foreign Affairs Committee who awaited his testimony Thursday.

The administration views the agreement as a breakthrough in cooperation amid rising tensions between U.S. and Russia over missile defense, NATO expansion and Iran. The deal would give the U.S. access to state-of-the-art Russian nuclear technology and help Russia establish an international nuclear fuel storage facility.

It is not clear whether congressional opponents have the votes to block the agreement.

Rood, in testimony prepared for the hearing and obtained by The Associated Press, acknowledged the opposition. But, he said, it was "a good, solid agreement" that "contains all the necessary nonproliferation conditions and controls that Congress has written into law."

He compared the agreement with those in effect involving China, Japan and the European Atomic Energy Community, which codifies cooperation with the 27 member states of the European Union.

Such an agreement with Russia is important, according to Rood's testimony, "both to build a closer relationship as well as to improve our ability to address major challenges we face in the 21st century."

Bush's notification to Congress on May 13 began a process to complete the deal. The agreement will take effect unless both the House and Senate pass resolutions blocking it within 90 working days.

Among the opponents are the committee's chairman, Rep. Howard Berman, D-Calif. The committee's top Republican, Rep. Ileana Ros-Lehtinen of Florida, and 13 GOP colleagues asked Bush to withdraw the deal.

Opponents believe Russia is not doing enough to help prevent Iran from developing nuclear weapons and should not be rewarded. Some also are critical of Russia's human rights record.

Lawmakers would have to pass the resolutions by two-thirds majorities to avoid a presidential veto. Lawmakers could pass legislation, however, that would hinder the administration or its successors from putting the deal in place, either by withholding money or imposing restrictions.

Members of Congress also are exploring whether the administration made a clerical miscalculation that could kill the deal. A report by the Congressional Research Service that was requested by an aide to Ros-Lehtinen found that the administration may have informed Congress too late to meet the requirement for 90 days of consideration.

The agreement would be a boost for efforts in the United States to step up nuclear energy development. It has slowed drastically since the 1979 accident at the Three Mile Island plant in Pennsylvania.

The deal would help Russia in its efforts for a nuclear fuel storage facility. It cannot achieve that goal without signing the deal because the United States controls the vast majority of the world's nuclear fuel.

Work on the agreement began after former Russian President Vladimir Putin and Bush promised in 2006 to increase nuclear cooperation.

The Bush administration has criticized Russia for providing nuclear fuel for Iran's Bushehr power plant, which Iran says is part of a peaceful nuclear energy program. The U.S. also has struggled for Russian approval of penalties against Iran in the U.N. Security Council for Iran's refusal to halt uranium enrichment. Still, Russia has voted in favor of three rounds of penalties.

Rood cited the Bushehr plant in his prepared testimony. "The administration examined this issue closely and determined that the steps Russia has put in place in its agreement with Iran mitigated our concerns."