Budget realities have clipped the wings of the Air Force's plans to have the National Aero-Space Plane reach orbit and fly 25 times the speed of sound, an official said.

The experimental hypersonic craft's top speed will likely be cut from Mach 25 to Mach 12 or Mach 15 and its runway-to-space approach may be abandoned in favor of launch from the back of another airplane, Air Force Maj. David Thurston said Monday."Congress is making difficult choices in an era of declining budgets," he said. "The bottom line is that it's going to be a suborbital craft."

Plans for a plane that can take off and land as usual but reach orbit have been an emblem of U.S. commitment to advanced technology. While European nations, including Russia, are working on a similar plane, post-Cold War budget realities made the Air Force reassess its vision for the craft.

Debate over the arrow-shaped plane increased as its projected cost soared from $5 billion to at least $10 billion. It will now be cut to the politically more palatable $3 billion range, Thurston said.

Fiscal 1993 funding for the space plane was cut from a requested $255 million to $150 million.

The plane also will be reduced to about a third of its size. It had been designed to be about 165 feet long and 50 feet wide.

The scaled-back program was first reported Saturday in the Los Angeles Times, which quoted an official of a company building the plane as saying the Air Force's decision was disappointing but understandable.

Rockwell International Corp. is developing the plane as part of a team that includes General Dynamics Corp., McDonnell Douglas Corp. and United Technologies' Pratt & Whitney unit.

Sam Iacobellis, Rockwell executive vice president, said that even scaled back the plane can achieve breakthroughs in materials and propulsion technology. He predicted the United States will eventually return to the goal of a runway-to-space plane.