The authors of a U.S. program designed to secure weapons of mass destruction in the former Soviet Union say they worry that deteriorating relations between the United States and Russia could undermine efforts to keep the weapons out of the hands of terrorists.

Sen. Richard Lugar and former Sen. Sam Nunn say the two countries have continued working together to secure nuclear, chemical and biological weapons despite growing hostility after Russia's invasion of Georgia last month.

They said in separate interviews with The Associated Press, however, that the spike in tensions heightens the risks of a breakdown in the arrangement under which the United States pays for the program.

"The Nunn-Lugar program has survived the very bad feelings between the U.S. and Russia before," Nunn said. "History is full of examples where pride and dignity basically overruled self-interest."

The Nunn-Lugar Comprehensive Threat Reduction Act is credited with funding efforts helping Russia and other former Soviet republics to destroy, dismantle and secure thousands of nuclear warheads and other weapons of mass destruction.

Lugar, R-Ind., and Nunn, D-Ga., pushed for passage of the program in 1992 as the Cold War was ending and the fractured, weakened former Soviet republics had few resources to secure their stockpiles.

The current concern comes as Russia and the United States have begun to draw down cooperation on many fronts. The United States already has suspended joint military programs and withdrawn an agreement for civilian nuclear cooperation that it had hailed previously as a breakthrough. It has promised further action.

Russia, in turn, has hinted that it could halt cooperation on efforts to rein in Iran's nuclear program. Even before the Georgia conflict, Russia suspended participation in a major European treaty that limits the deployment of tanks, aircraft and other heavy weapons across the continent.

Lugar expressed his misgivings to the AP following a hearing of the Senate Foreign Relations Committee on Georgia. During the hearing, he questioned Undersecretary of State William Burns, a former ambassador to Moscow, on cooperation with Russia. Lugar said he was reassured that the Bush administration seemed committed to working with Moscow to secure WMD materiel.

"Of course I'm concerned," he said. "I believe this work is in both countries' interests, and it is important for some of us to keep pointing that out."

Burns testified that the United States would work with Russia when it made sense.

"We are likely to have a relationship with Russia for some time to come which mixes competition and political conflict with cooperation," said Burns, the third-ranking U.S. diplomat. "Nowhere is our cooperation and our leadership more important than in the whole complex of nuclear challenges."

Casey Ruberg, a spokeswoman for the National Nuclear Security Administration, which oversees part of the Nunn-Lugar-funded programs, said the agency has not seen any slowdown in work from either side.

Some analysts in Russia say Moscow is unlikely for now to end cooperation on dismantlement and nuclear security because it values U.S. technical assistance and understands the need for the programs.

"It is not in America's or Russia's interest to stop cooperating," said Alexander Konovalov, president of Institute of Strategic Assessment, a Moscow think tank. "Keeping these weapons out of the reach of terrorists should be more important than political disagreements."

Others are less sanguine.

"I have not seen any effects from the ongoing tensions between the two countries, but I expect to see a change for the worse soon," said Fyodor Lukyanov, editor of the Moscow-based Russia in Global Affairs magazine. "There is no trust between the two countries now, there is only suspicion."