Defense Secretary Caspar W. Weinberger parted the secrecy curtain slightly on the new Stealth bomber yesterday by declaring that it would not cost much more than the existing B1 in inflation-adjusted dollars. But his figures failed to satisfy critics demanding fuller disclosure about Stealth's cost and technical questions.

"The total estimated cost for research and development and procurement of 132 ATB [advanced technology bomber] aircraft is $36.6 billion in fiscal 1981 dollars" which "compares favorably to the estimated $26.5 billion" for the B1 in 1981 dollars, Weinberger said.

"Thus," he continued, "the estimated average cost per B1B is $265 million and the cost of the far more capable ATB is $277 million for each aircraft. The ATB program is on schedule, the technology is well understood and working, and we expect the system to be operational in the early 1990s."

The Stealth bomber, as the ATB is commonly called, is believed to be shaped like a flying wing with rounded surfaces to minimize the reflection of radar beams, making it difficult to detect in flight. Weinberger said the stealthiness of the bomber "is based on a very robust technology that will allow it to penetrate advanced Soviet defenses and ensure its effectiveness well into the 21st century."

Weinberger has rejected suggestions from Rockwell International Inc., builder of the B1, and the bomber's congressional backers, to continue B1 production after the 100th one is delivered in order to allow further evaluation of the Stealth. The Northrop Corp. is building Stealth.

With the administration's refusal to buy more than 100 B1s, the political fight over how many of each bomber to build is centered in Congress. Rockwell and its champions will try to add money to the pending fiscal 1987 defense budget to force the administration to buy additional B1s.

Rep. Mike Synar (D-Okla.), who has Rockwell workers living in his congressional district but said he has not made up his mind on the bomber battle, said Weinberger's four-paragraph "fact sheet" on the secret Stealth program did not give lawmakers enough information to make informed judgments. He said the cost of the Stealth in the future, not what the bomber would have have cost in fiscal 1981, should be released and that any technical doubts explored publicly. Synar estimated that with inflation and other anticipated increases for Stealth, 132 bombers will cost $75 billion.

"If the Pentagon is now so sure of the technology," Synar said, "Congress should demand that the Pentagon put a cap on its ultimate cost as was done with the B1."

The Pentagon in the last paragraph of its Stealth release echoed the Central Intelligence Agency and National Security Agency by advising the press about how it should handle sensitive information the government chooses to release:

"Release of the above information should in no way be considered a relaxation of the necessary security procedures associated with the program. To the contrary, we remain thoroughly committed to protecting any and all information that would aid the Soviet countermeasure effort. Accordingly, we think it would be very much against the national interest to make public additional information or data about the aircraft. It would aid the Soviets and no one else."