It would be "relatively easy" to destroy Soviet short-range missiles flying toward Europe with a laser beam reflected off a mirror launched shortly before the attack, Edward Teller told NATO defense leaders here.

Teller, who helped develop the hydrogen bomb, discussed the "pop-up mirror" in trying to assure Europeans that President Reagan's Strategic Defense Initiative -- or "Star Wars" program -- would not erect a missile umbrella over the United States alone.

The first payoff of SDI research, Teller said during the Wehrkunde conference here over the weekend, might well be in finding a way to shield Europe from the Soviet SS20 missile and rockets of shorter range. One reason that stopping such missiles "is relatively easy," Teller continued, is that their fuel tanks are extremely vulnerable to destruction shortly after launch.

Expanding on his idea in an interview, Teller said the mirror would be launched 50 to 100 miles above Earth at the first warning of a Soviet missile attack on Europe.

He said the mirror would be less vulnerable with this pop-up tactic than if it were stationed in orbit. A ground-based laser, Teller said, would bounce beams off the mirror. The mirror would be effective even as it was being rocketed out of the atmosphere, he said.

"This is of some great technical interest in Germany," Teller said, because of the nation's advanced optical industry, which could coordinate the laser beam and mirror in developing a European missile defense.

Declaring that it would take only a few years to put such a system together, Teller said: "I would like to demonstrate" the antimissile defense system "before President Reagan leaves office."

In sounding another optimistic note about the potential of an effective missile defense, Navy Secretary John F. Lehman Jr. told Wehrkunde delegates that the U.S. Navy's Aegis cruiser air defense system had managed to destroy 15 out of 16 simulated cruise missiles in a recent exercise.

The Aegis' capabilities, Lehman said, have "totally transformed the naval balance in Europe." He called for a "Naval Defense Initiative" that would add Aegis technology to NATO warships "to bring Europe with us into the 20th Century."