They have introduced an amendment to an energy spending bill that would cut the $6 million President Bush is seeking for research on nuclear weapons with a yield of less than five kilotons, about one-third the size of the bomb that the United States dropped on Hiroshima.

Senator Dianne Feinstein of California says the administration's proposal sends the wrong message, at a time when the United States is trying to persuade Iran and North Korea not to build nuclear weapons. "We may very well be encouraging the very nuclear proliferation we seek to prevent," she says.

The administration says it is only interested in research on the weapons, not deploying them.

Republican Senator Jon Kyl of Arizona says the administration plan could provide an important tool in the war on terrorism. "What kind of nuclear deterrent should we have? What this amendment would do is stop us from even thinking about that. It seems to me we ought to be thinking about that," says Senator Kyl. "And, if smaller, more precise weapons could do the job just as well, wouldn't people of good will who are concerned about unnecessary death be interested in at least thinking about weapons that would pose a deterrent to an attack, but would not kill as many people, would not kill so indiscriminately?"

The Senate is expected to vote on the amendment Tuesday. The measure also includes a provision to cut $15 million for an earth-penetrating nuclear warhead for use against deeply buried bunkers.

Earlier this year, the Republican-led Senate lifted a decade-long ban on the study and development of low-yield nuclear weapons, turning aside Democratic objections. But lawmakers did agree to require the administration to get congressional approval before building any.

The House of Representatives has voted to cut nearly all funding for the program.