Behind Melvin B. Zisfein a hot-air balloon was moving up and down. Tethered over an electric coil, the balloon filled up with heated air that sent it nearly to the ceiling of the National Air and Space Museium. Meanwhile, as Zisfein talked, the smaller balloons on his tie moved up and down.

"You can never have too many balloons," the museum's acting director said.

The balloon, 15 feet in diameter, is only a small part of the museum's new "Flying for Fun" gallery that opens today at one end of the first floor. Included in the exhibit are kites, hang gliders, sailplanes, boomerangs, model airplanes and a complete history of the Frisbee - from a baking tin made by the Frisbie Pie Company to the latest Wham-O Super Pro.

"So much of the museum is high technology, and you can't really fly any of it without a background in science and technology or an expensive , time-consuming training course," said curator Claudia Oakes. "We wanted something people could just go out on a summer afternoon ad do."

The only exception to the no-high-technology rule is a 1928 Aeronca C-2, which Oakes described as "the Cessna of its time - the first plane people could easily afford and go out and have fun in."

Also on display are the first aeronautical objects acquired by the Smithsonian - elaborate kites donated by the Chinese embassy in 1976. The exhibit, a year in preparation, will run all summer.