It used to be that you could tell an aerospace engineer by the pink slip sticking out of his pocket. Now they are so scarce that defense firms are paying bounties to steal them from one another. A simultaneous jump in defense and airliner business has Texas Instruments running ads in Los Angeles extolling the virtues of Dallas, Northrop offering $1,000 in cash for new workers, and Boeing hiring overseas for the first time in a decade. The Commerce Department predicts that the aerospace companies will sell $47 billion worth of missiles, planes and other hardware this year, a 20 percent jump from 1978. That increase, combined with new airliner programs at several companies, has created the tightest market in years. "When we're in sync with Douglas, Rockwell and Hughes, that's what causes problems," says a Lockheed spokesman. "If it's timed so that when we're hiring, Hughes is laying off, that's beautiful. But if needs are the same across the board, there's just not enough people to meet demand." Lockheed has added 6,000 employes in the past year for its £1011 program; Boeing has hired 631 engineers permanently and 553 temporaries. Lockheed has paid out $45,500 in bounties, and Northrop several hundred thousand dollars in its "Refer a Friend for a Career at Northrop" program.