When U.S. fighter jets tangled in a mock battle called Copper Flag in central Florida two years ago, Air Force officials were chagrined to find that more than one-third of the planes were "killed" by their own forces.

In official Air Force jargon, such friendly fire is known as fratricide. In pilots' slang, the victims "mort themselves out."

Whatever the term, the nightmare of comrades unwittingly shooting one another is just one of the hazards in today's high-speed, high-tech world of aerial combat. The blue yonder has changed enormously since fighter jocks of an earlier generation fought in Southeast Asia, and tacticians here at the Fighter Weapons School -- the Air Force graduate school for its best pilots -- are searching for ways to increase the survival odds.

Combat planes now look so much alike, move so swiftly and fire from such distances that a pilot's most dangerous enemy might be his buddy. Furthermore, air defenses are much more intense than they were in Vietnam, as U.S. losses in Lebanon and Libya illustrated. A two-man team from Nellis is in England studying the April 15 raid on Libya for lessons about the Soviet-built surface-to-air missiles, SAMs.

Aerial warfare looks a little different -- a bit less predictable -- to pilots here than it does to official Washington. In the aftermath of the Libya raid, notwithstanding damage to the French embassy in Tripoli and other unintended targets, there was much rhetoric from the Pentagon and White House about precision bombing and minimal "collateral damage" to civilians.

"We say we can attempt a surgical strike, but jeez . . . ," said Col. Richard E. Guild, vice commander of the 57th Fighter Weapons Wing. "The precision munitions we have now have very good capabilities, but you can't be sure nothing will go wrong."

Even in the Nevada desert, where conditions are often "clear and 40" -- meaning 40 miles' visibility -- a slight increase in humidity can halve the range of infrared target finders. Lasers used to guide munitions can be disrupted by smoke or clouds. Bombs have been known to bounce off the desert floor, or "go slick," by failing to deploy braking vanes that are crucial for accuracy.

"You can't predict the kinds of things that happen on our big ranges," said Col. Richard Myers, commandant of the Fighter Weapons School. "That's why we have big ranges."

There is one thing pilots say has not changed much since Vietnam: Politics is a wingman. "The Libyan action was a political statement" by hitting targets alleged to have terrorist connections, said Lt. Col. Gary D. Kanikeberg, the F15 division commander here.

"The Israelis in Lebanon in 1982 made a military statement, so they rolled up that air defense and then just flattened the Syrian tanks," he said. A similar, purely military strategy in Libya "wouldn't start with the targets we started with. We'd go after the systems that were a threat to us" by first destroying Libyan air defenses.

But political restrictions have become part of the landscape in combat, added Lt. Col. G.L. (Scar) Scarborough, the F16 division commander, and "you just hope they give us enough latitude that we can go in without it becoming a suicide mission."

The tactics of Vietnam increasingly are consigned to the archives, behind the locked gate of the library here that contains the classified records of every U.S. bombing raid in Southeast Asia.

There are only a half-dozen combat veterans among the 60 or 70 pilots at the Fighter Weapons School. Their planes, notably the F15, F16 and A10, also are post-Vietnam, with only the F111 surviving from an earlier generation.

In Vietnam, where more than 2,500 U.S. planes were lost in combat, pilots had only one kind of SAM to worry about. Today, there are as many as 15 variants that fighter jocks must know intimately, each with unique range, electronic signature and lethal characteristics. Among the SAMs fretted over are American-made Hawks, which Iran possesses, and French-made Rolands, which are sold to a number of potential adversaries.

More than a decade ago, pilots trained to dogfight in Vietnam "two v. two" -- two U.S. planes versus two enemy planes. Today, given the Soviet bloc's overwhelming numerical advantage, the pilots practice "two v. eight" or "four v. 12."

If modest raids on Third World nations are unpredictable, tacticians here admit that there are huge uncertainties in trying to prepare pilots for a modern war with the Soviet Union.

"Nobody really knows what it's going to be like that first day of a major war when you fly into the valley and your wingman dies before you've ever fired," Kanikeberg said. "You might say, 'Whoa!' and turn around and go home. But we'd like it to be Ivan who says that."

One problem that instructors face is that today's munitions are so expensive that it is common for even experienced pilots never to have fired some of the most important missiles in the arsenal. For example, only about one-third of the A10 pilots arriving at the Fighter Weapons School have launched a $240,000 Maverick missile, according to Lt. Col. Coy D. Fink, the A10 division commander.

Nevertheless, senior officers here think that young pilots are "better prepared for the fog of war" than they were during the Vietnam war when "anybody could be a fighter pilot," as Myers put it.

"We're not trying to teach 'top guns,' " he added, referring to the movie now showing around the country. "There's no top gun here. And no heroes. . . . We don't do heroes."

Still, the traditional swagger of confidence that has been part of the fighter pilot's myth since the days of Eddie Rickenbacker has by no means vanished. Particularly when it comes to sizing up the creativity and initiative allowed Soviet airmen, the pilots here affect a jaunty insouciance about Ivan.

"The good news in the American military is that the entrepreneur is alive and well," Myers said. "I don't know much about the Soviets, but there doesn't seem to be much of a premium placed on entrepreneurship.

For the past quarter century, much of the mulling by tactical mavens has been in search of the best altitude to attack enemy targets and live to brag about it.

Some of the first bombing raids in Vietnam were flown at the treetops, but "at those altitudes everybody and his brother could shoot at you," Guild said. Pilots moved to higher altitudes, but "in the late '70s and early '80s, we were driven down to the dirt" by increasingly lethal SAMs, he said.

That meant flying at 100 feet or lower, Guild added, and "you realize you're not going to live very long doing that." It takes talented pilots about 300 flying hours of practice to fly proficiently in the 300 to 500 foot altitude "block," but another 300 hours to be able to fly below 100 feet. Despite the greater reliability of today's planes, such tactics still made the cockpit a dangerous place.

Consequently, "we're walking the dog back to mid-altitude combat," Guild said. The Air Force made a "corporate decision" to adopt a tactic called SEAD -- Suppression of Enemy Air Defenses -- which calls for "rolling back the umbrella" of enemy air defenses by jamming radars and attacking the most lethal SAMs first.

"We're also devoting a lot of attention to electronic warfare, to disrupting his command and control," Guild said. "That's the doctrine we're in now: How do you put the strike package together?"

In a battle with the Soviets, the plan calls for making superior Soviet ground forces vulnerable by crushing their air defenses. To overcome the huge number of Soviet fighters, U.S. pilots are expected to win against poor odds. For example, an F15 pilot's "contract is to kill two at the merge," Kanikeberg said, which means that before the adversaries pass one another, the U.S. fighter must destroy two enemies.

"In the F15 world," Kanikeberg added, "our attitude is that we're the biggest airplane, we're the king of the valley, and we're coming into the valley."

The Soviets are assumed to possess an "all-aspect" missile that can be fired head-on at an adversary without having to maneuver behind him as before. To be successful, U.S. pilots probably must fire their long-range missiles on the basis of radar information without "visual confirmation." That can lead to fratricide, which Myers said "is going to be a tremendous problem."

Whether shooting without eyeballing the enemy will be allowed, as Scarborough noted, will be another tough political decision.

"Day one, Central European Region, it's going to be an awesome battle," Kanikeberg added. "Lot of losses."