Air Force leaders in today's prodefense environment are pressing Defense Secretary Caspar W. Weinberger to buy two new bombers at once, one an update of an existing plane and the other the radar-elusive Stealth.

But Weinberger, Air Force officials said, is holding off on any such commitments until he satisfies himself that the development and production of a Stealth bomber cannot be accelerated without risking technical problems and cost overruns.

He is scheduled to fly to Strategic Air Command headquarters in Omaha today to discuss strategic issues with SAC Commander Richard H. Ellis.

Gen. Ellis is an outspoken advocate of building an interim bomber for the 1980s until the Stealth can be developed for the 1990s and beyond. Ellis contends that the Soviets' nuclear strategic edge demands this quick-fix approach for the U.S. nuclear bomber force.

The two candidates for the interim role are an elongated version of the Air Force F111 already in service and a modification of the B1 bomber, which was developed to the point of being flight-tested but was not put into production.

The Air Force estimates that it could build 180 F111 bombers for between $7 billion and $9 billion and have these stretched versions flying by late 1984. Critics contend, however, that the F111 could be shot down by modern Soviet antiaircraft defenses.

Air Force advocates of building an updated B1, which would have less swing to its wings to save money, estimate that 100 of these penetrating bombers could be built for $17 billion to $22 billion.

One argument against this course is that such a huge amount of money would be better spent on a Stealth bomber specifically designed to penetrate the modernized air defenses the Soviet Union is developing.

The Carter administration concluded that neither the stretched F111 or the B1 bomber was worth building, given the effectiveness of Soviet air defenses, and opted for producing cruise missiles. These missiles would be fired from aircraft while still outside enemy defenses.

President Reagan during the campaign lambasted former president Carter for canceling the B1, and earmarked $2.4 billion in his fiscal '82 budget for some kind of new penetrating bomber. He has not specified what kind he intends to build, and missed the March 15 deadline for notifying Congress of his choice.

Now that the March 15 deadline has passed, some Air Force leaders are urging Weinberger to remain uncommitted about the type of bomber to be built until the costs of building Stealth are nailed down. The Air Force already is conducting discussions with defense contractors in hopes of arriving at reliable estimates.

Some Pentagon weapons specialists are warning Weinberger that building the Stealth bomber on a crash basis would invite technical problems and cost overruns. But sources said Weinberger is not convinced that this need be the case.