The Senate yesterday approved continued production of the B-2 "stealth" bomber by the smallest margin in the history of the controversial aircraft as it rejected moves by critics to kill the program or stall it for a year.

Senate approval for construction of two more of the costly, radar-evading strategic bombers improved chances for the program's survival in conference with the House, which is expected to vote next month to build no more than the 15 planes that have been authorized by Congress.

But the loss of 11 votes since the Senate voted on the issue last year indicated the future of the $62 billion, 75-plane program is shaky at best.

In the first of this year's key tests for the B-2, the Senate voted 56 to 43 to reject a proposal by Sens. Patrick J. Leahy (D-Vt.) and William S. Cohen (R-Maine) to kill the program and complete construction of only six planes that will be used for flight testing.

Then it voted 53 to 45 against a fallback proposal from Cohen and Leahy to drop production of the two bombers sought by the Bush administration for fiscal 1991 but provide the capability to resume production if Congress decided to do so after successful completion of performance tests.

Approved 97 to 2 were a series of conditions proposed by the Senate Armed Services Committee that would bar release of funds for the two new bombers until performance tests are successfully completed.

In votes on the B-2 last year, opponents mustered no more than 32 votes to kill the program. Critics did not expect to win a majority to terminate production this year but had hoped to come closer to winning on the production-freeze proposal.

Senate action on the B-2 was regarded as critical because the House is expected to go along with its Armed Services Committee and vote to kill the program after the currently authorized production of 15 bombers when it takes up the defense authorization bill in early September.

In contrast to the House panel's action, the Senate Armed Services Committee acceded to the administration's request and authorized $4.6 billion for the B-2 program in fiscal 1991, including $1.8 billion for two more bombers and parts to build another six. The committee insisted on a series of additional flight tests before the funds could be spent but did not challenge the administration's most recent plan for a fleet of 75 planes.

As recently as last January, the administration asked for 132 of the expensive bat-wing bombers, which were designed to evade Soviet radar detection and penetrate deep into the country to destroy critical targets in a nuclear war. In May, responding to easing of U.S.-Soviet tensions and pressures for military spending cuts, Defense Secretary Richard B. Cheney reduced his request to 75 aircraft, which had the effect of increasing the cost of each plane from $532 million to $865 million.

"The B-2 bomber was devised by strategic planners when the Cold War was hot and the defense budget was bulging . . . We cannot afford it and we do not need it," argued Leahy during yesterday's debate.

In a surprise move, Sen. John Glenn (D-Ohio), former astronaut and Marine Corps colonel who sits on the Armed Services Committee, joined Leahy and Cohen in calling for termination of the program, saying it is neither affordable nor necessary. Available funds should be going instead to manpower and conventional forces, said Glenn, who has grown increasingly skeptical of the B-2 program since voting to continue it last year.

But Minority Leader Robert J. Dole (R-Kan.) and other B-2 supporters contended that the Iraqi attack on Kuwait Wednesday night demonstrates the continuing risk of war and the need for advanced weapons in volatile, critical areas such as the Middle East.

"If we needed {Iraqi President} Saddam Hussein to give us a wake-up call, at least we can thank him for that," Dole said.

However, it was the plane's staggering cost -- and the losses that would come with its cancellation -- that drew the most attention.

"I'm afraid that if we continue to let this hemorrhage of dollars continue, this plane will be too expensive to fly," said Sen. Alan Cranston (D-Calif.), contending that the pricetag of each plane would approach $1 billion when operating costs are included.

But Armed Services Committee Chairman Sam Nunn (D-Ga.) said the largest expenditures have been made, meaning the United States will be getting more for its money as it completes the 75-plane fleet. With $27 billion appropriated and another $9 billion needed to complete the first 15 planes, another $26 billion will buy the remaining 60, he said.