The Smithsonian Institution's plans to have a remote-controlled model of a giant prehistoric flying reptile soaring over the Mall are on schedule.

The flight, announced last summer, is set for sometime next spring, and the only question still up in the air, so to speak, is whether the flying contraption -- a battery-powered model of a pterodactyl -- will be a life-sized re-creation or something a bit smaller.

"It will be the full-size, 36-foot version if we can get there, but we'll settle for half that," said Brian Duff, associate director for external affairs at the Smithsonian's Air and Space Museum.

A quarter-scale model has been tested successfully, Duff said, and a team of aeronautical engineers, robotics experts and paleontologists is hard at work building and testing larger ones. The $400,000 project, funded by Johnson Wax and the Smithsonian, is being designed and built by Paul MacCready, a California aerodynamicist whose experiments with pedal- and solar-powered aircraft are well known.

The pterodactyl (Quetzalcoatlus northropi) existed in various forms for about 145 million years and is believed to have become extinct about 60 million years ago.

Duff said building a flying model of the airborne reptile has taught scientists a lot about the creature.

Paleontologists, for instance, have scrapped earlier models of the beast and are building two new full-scale models.

"I'm afraid our own version in the Air and Space Museum may be somewhat flawed," said Duff. "We've reassessed the shape of the wing and the size of the body."

The museum also is preparing a new film that will examine the nature and evolution of flight. Its premiere is set for June 19, 1986, and the re-created flight of the pterodactyl is an important part of the film.

Duff said the pterodactyl's test flight in California -- rather than its flight over the Mall -- is the one that will be featured in the film because of differences in production schedules for the movie and the Mall flight.

After bringing back the pterodactyl, the Smithsonian will focus on its next flight project, already in the works at the Massachusetts Institute of Technology. For 1987, Duff said, the museum is planning to enact -- using a human-powered plane -- the flight from Crete to mainland Greece by Daedalus, who is credited in western mythology as having been the first mortal to fly.