The Senate this week is expected to vote on spending a relatively small amount of money – $15 million – that could have a large effect on the nation’s nuclear-weapons program and on international treaties. A proposal to research a nuclear bunker-buster, cut earlier but saved in the House, returns to the Senate just as India and Pakistan demonstrate that nuclear technology can spread and pose worldwide dangers in ways the United States cannot control.

The potential use of such a weapon was seen in Afghanistan, where al-Qaida members hid in deep caves and fortified underground structures. The U.S. military used the conventional burrowing weapon, called the GBU-28, to attack some of these positions, although its effect apparently was limited. According to news reports, there are some 10,000 underground facilities in more than 70 countries, with 1,400 holding weapons of mass destruction, ballistic missiles or military commands.

The idea of the plan before the Senate is that a smaller nuclear weapon would be able to push deep enough into the ground to destroy a target but without the ground-level blast and heat leading to the deaths of hundreds of thousands. Such a weapon would have to dig at least 200 feet down to achieve this but still would not keep the irradiated debris from flying, killing fewer but a still considerable number of people. In any event, the military’s most-likely weapon to date, the B61-11, hasn’t gone farther than 10 to 20 feet into a dry lake bed. The Senate would be voting on the development of a new weapon, called the Robust Nuclear Earth Penetrator (RNEP).

For decades the United States has been a leader in urging the ban of tests for nuclear weapons and, through the Non-Proliferation Treaty, from stopping their spread. For 25 years, the United States has pledged never to use nuclear weapons against enemies without nuclear capability. The importance of the $15 million in research is that, not only does it establish a permanent constituency for its growth, but it substantially changes U.S. policy, a change that will be followed elsewhere. As Presidents Bush and Putin announce nuclear-weapons reductions for long-range missiles, it is counterproductive to pursue a new class of weapons that are nearly as deadly, if they can be made to work.

Robert W. Nelson, a theoretical physicist who works on technical arms control issues and a member of the research staff of Princeton University, recently wrote, “The danger of moving from a conventional to a nuclear war is so enormous, that the U.S. refrained from using nuclear weapons in Korea even when U.S. troops were in danger of being overwhelmed. Attempts to develop a new generation of low-yield nuclear weapons would only make nuclear war more likely, and they seem cynically designed to provide legitimacy to nuclear testing – steps that would return us to the dangers of Cold War nuclear competition, but with a larger number of nations participating.”

Maine Sens. Olympia Snowe and Susan Collins are important votes on this issue. They should emphasize the need to reduce the threat of nuclear weapons worldwide over finding ways that would promote their use. They should vote against spending on the development of weapons with nuclear fallout that would endanger countless innocent people.