"If the Yugoslavs have done it, it's probably the military story of the century," Krepinevich said. "Based on one incident, I think it's premature to say stealth has been compromised."
Stealthy, Yes, but Not Invulnerable
But analysts also said that the Pentagon and Lockheed Martin have never maintained that the stealthy design and materials of the aircraft made the planes incapable of being hit.
"They have never claimed that stealth was perfectly invisible, only that it makes it much less visible than a normal airplane," said Lawrence Korb, director of studies at the Council on Foreign Relations, a New York think tank.
"You're going to get some shot down, but you're not going to get as many shot down as in the '50s and '60s," he said.
Also, the F-117A uses an early generation of stealth technology. The stealth features on the B-2, built by Northrop Grumman Corp. in Palmdale, and on the F-22 from Lockheed Martin and Boeing Co. are far more advanced.
In fact, Saturday's crash of the F-117A "may be an argument in favor of the F-22 because it does have a more advanced form of stealth," said Daniel Goure, deputy director for political-military studies at the Center for Strategic and International Studies in Washington.
Goure said it's unlikely the F-117A crashed because of mechanical failure, because "if that was the case, I would have expected the Pentagon to have said something by now. It would have been very reassuring to people worried about stealth's effectiveness."
But an "operating problem" could be the culprit, Goure said. The jet "is not equally stealthy in all conditions, for instance when it opens a bomb bay" and when it flies at low altitude, he said.
The F-117A also has had a reputation as a difficult plane to fly. At least two crashed while the aircraft was still a top-secret project in the 1980s. Another crashed during an air show in the suburbs of Baltimore in 1997.
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Sometimes Invisible, Sometimes Not
The F-117A Stealth aircraft is often referred to as a fighter but is basically a bomber that uses special non-reflective coating and design features to avoid enemy radar. It isn't entirely invisible, however. When the bomb doors open, it will show up big and bright on enemy radar screens. And during the 1991 Persian Gulf War, British radar operators claimed that the F-117As were detectable on Britain's older radar, which uses a long wavelength.
Stealthy but slow
Cost: $45 million
Number remaining: 56
Length: 66 feet
Wingspan: 43 feet
Height: 12 feet
Weight (fully loaded): 65, 800 lbs.
Range: Unlimited with air refueling
Builder: Lockheed Martin Corp.
When It's Vulnerable
By overlapping radar sites, Serbian radar operators can spot incoming planes at one site, then fire and track missiles at another.
1. Pilot levels out plane for optimal release of its two bombs.
2. When bomb bays open, the projecting doors give the F-117A a radar profile visible to enemy antiaircraft positions.
3. Pilot attempts to release bombs before enemy radar can lock on, then quickly closes bay.
4. Shoulder-carried missile launchers can also target F117A, but its infrared image is hard to read.
Sources: Jane's How to Fly and Fight in the F-117A Stealth Fighter, Adm. Eugene Carroll, Associated Press, Times staff reports; researched by CHRIS ERSKINE and REBECCA PERRY/Los Angeles Times