A WORLD FREE of nuclear weapons is an appealing dream, but the reality is that the atomic bomb will not disappear soon. As long as the United States possesses a nuclear arsenal and needs to deter threats, the warheads and bombs must be kept safe, secure and, if deployed, effective. This is a goal of a major U.S. effort to refurbish and extend the life of its existing weapons.

One of the oldest of them is the B-61 gravity bomb, first designed in the 1960s to be dropped over a target by airplane, either as a strategic weapon carried by long-range bombers, or as a tactical or short-range nuclear weapon in Europe. The Energy Department’s National Nuclear Security Administration has been gearing up for a “life extension” program for the B-61, which will replace old parts and add security systems and controls.

The B-61 life extension was estimated two years ago to cost $4 billion. Sen. Diane Feinstein (D-Calif.), who chairs the Senate appropriations subcommittee that oversees the program, announced July 25 that the cost has doubled to $8 billion, according to a new administration estimate. What’s more, Ms. Feinstein said, an independent Pentagon cost estimate is $10 billion. The project is still at an early phase, but it looks to be ambitious and complex, combining four versions of the weapon into one by 2017. The Air Force separately wants to add a new tail assembly to improve the bomb’s accuracy.

Cost overruns are nothing new, but this one raises some difficult questions. The number of refurbished weapons that will result is classified. Hans Kristensen of the Federation of American Scientists estimates that 400 will be made, of which about 200 would replace tactical B-61s now deployed with NATO allies at bases in Belgium, Italy, Germany, the Netherlands and Turkey. These forward-based tactical nuclear bombs were intended to deter a Soviet land invasion of Europe. That threat has gone, and so has the military mission for the bombs. If a nuclear deterrent is needed on the continent, the United States has other options. The sole remaining value of stationing the gravity bombs in Europe is political, to demonstrate that non-nuclear members are sharing in the alliance defense burden. Even that is being debated within the alliance.

Moreover, the tactical nuclear weapons could well be eliminated in a future arms control treaty with Russia, which possesses a much larger arsenal of them.

Congress and the administration should weigh the escalating costs against the mission of the B-61. Nuclear weapons have not been used in combat for 67 years — they are intended to deter. Who will be deterred by the refurbished B-61? Is the symbolism of deploying the nuclear gravity bomb in Europe worth the billions of dollars? Does it make sense to embark on a $10 billion program to refurbish a weapon that could be put on the table in negotiations with Russia a few years from now? In an age of scarce resources, such questions can’t be slighted.