The Northrop Grumman Corporation is building 21 of the planes at a cost of $44.7 billion. Some members of Congress want to keep the production lines open and build up to nine more of the planes, at a yet undetermined cost.

The B-2 was developed in the 1980's as a nuclear bomber. Its mission was to penetrate to the heart of the Soviet Union and drop missiles on Moscow. Its most striking technological feature was said to be its ability to evade detection by the Soviet Union's radars.

But no prototype was built, and the plane has experienced a series of technological setbacks during eight years of flight tests. It has never been used in combat.

The report by the General Accounting Office said that the Air Force is working on the problem with the B-2's sensitive skin, but that it is unlikely that the problem ''will ever be fully resolved.'' As a consequence, the plane requires climate-controlled shelters.

The bomber, which flies at sub-sonic speeds, like a normal commercial jet, is based at Whiteman Air Force Base in Missouri. That increases by many hours the time it would take for the plane to respond to a crisis overseas. The Air Force had intended to deploy it at bases outside the United States to reduce those flying times.

But no climate-controlled shelters for the B-2 exist abroad, preventing the plane from being stationed overseas.

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In the report made public this week, the accounting office said that during a year of tests ending in March, the B-2 bombers were able to perform their missions only 26 percent of the time. The failures were in large part due to the fragility of the B-2's skin.

Rainwater and humidity damaged the plane's surface, sending the plane back to its hangars for repairs and a new coat of stealthy skin, which cures properly only in a climate-controlled shelter. Moisture also collected in the B-2's ducts and valves, causing malfunctions and requiring repairs.

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Some of the plane's stealthiness sustained damage each time the aircraft flew, the report said.

The B-2 was developed in secret under the classified ''black budget'' of the Air Force. In 1981, the Air Force said it could build 132 of the planes for $22 billion. But after eight years it had spent that sum, and had only a single plane to show for it.

''The real problem with the B-2,'' Sam Nunn, the former chairman of the Senate Armed Services Committee, said in an interview, ''is that it was kept secret too long.''

After its unveiling in 1988, failed flight tests and the end of the cold war created problems for the B-2. Not the least was its cost. The plane's price tag roughly equals three times its weight in gold.

Then came the question of its performance. In 1995, the G.A.O. reported that ''the B-2 radar cannot distinguish rain from other obstacles'' and that its stealthiness was dubious.

Then came the question of its mission. The Air Force says the plane does not have to be used as a nuclear bomber; it can also carry conventional bombs for ordinary missions -- to blow up a bridge, for example. But during the first open Congressional debate over the bomber, in 1989, Senator William S. Cohen of Maine, now the Secretary of Defense, called that a ludicrous idea: like sending ''a Rolls-Royce down into a combat zone to pick up groceries.''

Though the Pentagon says it does not want or need any more B-2 bombers, the plane has always had strong defenders in Congress, including Floyd D. Spence, a South Carolina Republican and chairman of the House National Security Committee. During that first open debate in 1989, Mr. Spence said the plane's cost was irrelevant, given its power to defend the United States from its enemies.

''Cost?'' he asked. ''What price tag do you put on freedom?''