Airline passenger traffic will recover from this year's poor showing and show moderate growth into the 1990s, the Federal Aviation Administration said in its annual aviation forecast. As a result, more funds will be needed to expand the national air space system and to pay for new facilities and equipment. The report noted that sharply rising fuel prices and a sluggish economy is fiscal 1980 held the industry at almost the same level as fiscal 1979. But air carrier passenger traffic is expected to improve in 1981, with a 21 percent increase between 1980 and 1992. The burgeoning commuter industry, which recorded a 14 percent gain in passenger traffic in fiscal 1980 despite the recession, will grow at an even faster rate than the big airlines.