The Pentagon included the request in its fiscal 2004 defense budget request. Within the request is a provision to repeal a 1994 law banning research and development of nuclear weapons with yields below five kilotons.
Democrats expressed concern the administration's request would harm U.S. credibility internationally on arms control and nonproliferation issues.
"This ban has been a pillar of arms control for the past decade. I consider it completely irresponsible of us to be asking for this now considering the fact that we are attempting to disarm other people around the world," said Rep. Ellen Tauscher, D-Calif., in a hearing yesterday of the House Armed Services Subcommittee on Strategic Forces.
"I think it has great potential to harm what little credibility this administration has left on arms control," she said.
The text of the proposal suggested the repeal is needed in part for national security reasons, to be able respond to challenges in international security, and to train young scientists.
An Energy Department official advocated the repeal Thursday at the House hearing.
"I do support repealing the legislation," said Everet Beckner, deputy administrator for defense programs of the National Nuclear Security Administration.
"The reason for that is primarily one of it's causing us to stop some analyses from occurring, which is a natural extension of work that you would do at higher yields," he said.
Tauscher asked whether research prevented by the ban has ever harmed the national security of the United States.
Beckner said, "I think to date it has not. But looking to the future I'm not certain."
Under questioning, Beckner also said the U.S. national laboratories lately were having "great success" in making new hires from universities.
The Pentagon may seek the option of using the low-yield warheads, experts said, for striking deeply buried and hardened underground bunkers, and also possibly for striking enemy chemical and biological weapons sites, with the idea the extreme heat from the blast would destroy the dangerous properties of those weapons.
Critics have charged the blast from the weapons would be harmful to any nearby populations, would be questionably effective and would break the taboo of using nuclear weapons.
Beckner said further research is required to know whether the weapons might work as hoped against chemical and biological agents.
"We know that we have to understand much better in the future how you destroy chemical and biological agents, as opposed to disbursing them. … As we study the problem more fully, we realize how difficult it is, specifically to kill biological agents," he said.
The requested repeal comes as the Bush administration is preparing for a possible war on Iraq in part because of Baghdad's pursuit of nuclear weapons in violation of the Nuclear Nonproliferation Treaty. The administration is also handling a crisis with North Korea, which withdrew from the treaty in January.
The United States is one of five countries allowed to possess nuclear weapons by the treaty, but those five agreed to make good faith efforts toward total nuclear disarmament over time.
Tauscher asked Beckner, "What do you think the ramifications would be if we repealed this ban to our credibility in the world that we are actually committed to arms control, to removing weapons systems not increasing systems, and that we are not kind of talking out of both sides of our mouths [when the United States] is attempting to prevent other people from getting nuclear weapons?"
Beckner said his job as a scientist was not to address such questions, but rather is to "assess the threat to the country and propose solutions."
Rep. Heather Wilson, R-N.M., who released a controversial report last month urging the repeal, said she thought it was "an illusion to think that we would be safer if we don't let people think about, explore things that we might find frightening, because they would never be able to come back to us with options."