Mars looks like the rocky coast of Maine, moved to the desert and painted red. There are huge trenches where sophisticated machinery has been rooting around. "Big Joe" is a famous Martian boulder. And Valles Marineris, the largest known canyon in the solar system, is four times deeper than the Grand Canyon and 10 times as wide. You could put the whole U.S. into it and have room left over for a concession stand.

All this and more may be inferred from the Air and Space Museum's new exhibit, "The Viking View of Mars," where postcard views of the planet are marred only by the leg of the Lander which keeps getting into the act. Scenery displayed on a computer terminal, in black-and-white and in color, is almost as good as science fiction.

Viking's view was live for three Martian years, from its landing in 1976 until mid- November when it went on the fritz. Perhaps the batteries died, a dust storm overpowered it, the transmission was lost somewhere in between or something pulled the plug -- though no footprints or scary shadows show up on screen. Scientists aren't sure which way the antenna is pointed, says exhibit curator Ted Maxwell, "But they've been trying like hell the past few months to get it back, just saturating Mars with powerful signals."

If Lander gets on the beam again, the museum is prepared to interrupt the computer's regularly scheduled programming to go live from the surface of Mars, 460 million miles away (after a five- to seven-minute delay from deep space).

For now, visitors ease into the exhibit with a Buck Rogers cartoon, a first edition of H.G. Wells' The War of the Worlds from 1898 and other sci-fi comic books. Then comes science: data on the surface composition, weather reports and life-seeking experiments: "No conclusive evidence for life on Mars has yet been found." One display -- for computer groupies only -- diagrams the linkups from deep space to tracking stations in California, Spain and Australia, all the way to the Air and Space Museum. A model of the prime computer is included. The real computer hums in an out-of-the- way office, its downlinks safe from dust.

Color patches and the American flag on the Lander were used to calibrate colors for the transmission. These, the cameras and earth-sampling machinery are visible on the Lander model downstairs, which has been on view for a couple of years. But the pictures are the heart of the new show. Even the shadows are sharp, since there's so little atmosphere in the way.