IMAGINE WALKING into a movie theater and suddenly finding yourself in the middle of a startlingly real battlefield. Guns roar on all sides. Tanks thunder along ahead of you. On each side of you, soldiers creep through mud. A machine gun crackles behind you. In the corner of your eye you catch a glimpse of action and turn to see a hand-to-hand encounter so close to your left side you'd swear you could reach out your hands and touch the combatants.

That's the experience some movie-goers will have this fall. The biggest revolution in motion pictures since the advent of sound will emerge from a laboratory on Long Island, N. Y., where it has been under development for several years. Already two theaters-one in New York, another in London-are equipped for public showings. Equipment for two more is all set for installation. Production films are ready to start rolling. Its developers hope that eventually it will become the movie makers' answer to TV.