The Smithsonian Institution's Air and Space Museum has received the estimated $400,000 in corporate donations needed to insure that a life-sized, remote-controlled model of a pterosaur, or flying dinosaur, will be soaring over the Mall by summer of 1986, barring any technological snags.

The Smithsonian had announced the project last summer with the caveat that it would need corporate funding to make the project fly.

"We'd always planned to do it, but now we can be sure it will be built on the scale that we wanted," museum deputy director Don Lopez said yesterday. The Smithsonian frequently relies on corporate funding for such projects, Lopez said.

S.C. Johnson & Sons, better known as Johnson Wax, will pay for the construction of the giant pterosaur, a project that is expected to cost approximately $400,000, according to Lopez. In addition to its flights around the Mall, the model will be seen in a new museum film, also sponsored by Johnson Wax, about the history of natural and human flight.

The pterosaur (silent p) existed in various forms for about 145 million years, and is believed to have become extinct 60 million years ago. The few fossil remains that have been found show the creature had a long neck, large head and a wingspan of 25 to 40 feet. The larger reptiles are thought to have weighed about 150 pounds.

Scientists have speculated for years that pterosaurs did more gliding than flapping and the museum hopes the model pterosaur will generate publicity for the film as well as help scientists learn whether the existing skeletal models, which have been constructed from relatively few fossil remains, are accurate.

The Smithsonian has given the task of designing and building the model to Paul MacCready, a prize-winning California aerodynamicist whose experiments with pedal- and solar-powered aircraft are world famous. His Gossamer Condor, a lightweight pedal-powered plane, hangs in the Air and Space Museum. Another pedal-powered plane, the Gossamer Albatross, flew across the English Channel in 1979.

MacCready and a team of experts in paleontology, bird flight and aerodynamics are experimenting in California with a small, glider version of the pterosaur. Plans call for the final version to weigh about 125 pounds and have a wingspan of 36 feet, roughly the size of a four-person airplane. It will be constructed of graphite, carbon and epoxy fibers.

The challenge, a Smithsonian spokesman said yesterday, will be to design a computerized "brain" for the model to simulate the slight, constant wing movement that the pterosaur is thought to have used to maintain its balance.