Study Says B-2 Can Carry Out Its Mission : Defense: But the secret report to Congress fails to answer questions about the Stealth bomber’s cost and usefulness. The Soviet response also is unknown.

A classified study prepared for Congress concludes that the B-2 Stealth bomber probably will be capable of carrying out its intended mission of penetrating Soviet air defenses, but it leaves unanswered questions about the plane’s steadily rising cost and what the Soviets are likely to do to counter it, sources said Thursday.

The Defense Department study, presented to the Senate Armed Services Committee in closed session Thursday, also does not address whether the plane’s stated mission--to attack Soviet command bunkers and mobile missiles--is realistic in light of evolving superpower relations and emerging technology.

The report was delivered shortly before Congress begins debate on the 1991 defense budget and coincides with a chorus of criticism of the B-2 as overly expensive and potentially irrelevant. The aircraft, developed by Northrop Corp. of Los Angeles, is expected to cost $825 million per plane.

“The plane is apparently very successful. It does what you want it to do,” said a Senate aide familiar with the study’s findings. “But this report doesn’t look at cost and need. Those are political decisions.”

Despite widespread misgivings about the B-2, Congress last year approved funding for the $62-billion program on the condition that the Defense Department report back periodically on a number of unresolved questions about the radar-evading bomber.

The Pentagon was required to create an independent study panel of scientists from federally funded research centers to determine whether the B-2 can carry out its mission, whether that mission makes sense, what the Soviets are likely to do to defeat it, how long the plane will remain useful and whether it is worth the money.

Only the first question was addressed in the report delivered Thursday. The panel is expected to present findings in the other areas later this year.

The report assumes production of a fleet of 132 Stealth bombers, the number originally proposed by the Air Force. It does not assess the effectiveness of the reduced fleet of 75 planes that the Pentagon now plans to build.

The scientists were given access to top secret Air Force data on the plane’s design and to intelligence estimates on Soviet air-defense capabilities. The assessment of the bomber’s performance was based on computer models and laboratory experiments rather than actual test-flight data.

Air Force Secretary Donald B. Rice said in an interview Thursday that, although the plane has not been tested against real radar, “nothing that’s gone on in any tests . . . gives us any reason to contradict the models.”

The panel reported to the Armed Services Committee that, given current and projected Soviet air defenses, the B-2 should be able to get through and attack its targets from close range with bombs and missiles.

The panel reportedly concluded that Soviet ground-based and air-based radar would not be able to detect the futuristic bomber, which the Air Force says has a radar “signature” no larger than that of an insect.

However, the study said that some B-2s would be lost in a large-scale attack on the Soviet Union because they would be visually spotted by Soviet pilots or anti-aircraft crews.

“Nuclear war fighting simply has no reality in an era of sharply declining tensions with the Soviet Union,” said Henry W. Kendall, professor of physics at the Massachusetts Institute of Technology and chairman of the Union of Concerned Scientists. “The B-2’s mission is changing constantly. The program should be terminated promptly.”

Staff writer Melissa Healy contributed to this story.