NEIL ARMSTRONG has described the vehicle scheduled to be launched this morning from Cape Canaveral as a "space truck." That is precisely what the shuttle is designed to be -- a vehicle that carries freight as well as human beings into space on a regular timetable. If all goes well, a shuttle like the Columbia will leap from Earth every two weeks or so by the mid-1980s, circle the globe while its crew does a job and then sweep down to a landing strip where it will be washed, greased and gassed up for the next flight. Just like a truck.

But there is a difference. If this weekend's flight and the other tests during the next 18 months are successful, this new space truck will open a future that cannot yet be clearly seen. The operations it will make possible are so varied that they bring all the wildest dreams of the space visionaries a giant step closer to reality.

The shuttle can -- and will -- be used early on as an orbiting scientific laboratory that will add immensely to our knowledge of the universe. It can become, at a later time, a manufacturing plant in which objects, such as ball bearings, are produced more precisely than they are on Earth.

The shuttle can be a repair vehicle, carrying the men and equipment needed to install new satellites, fix damaged ones and bring down those no longer useful for their assigned tasks in communications and surveillance. It can also be the cargo vessel of the future that carries the material with which space platforms are built and then ferries the crews and supplies for them from Earth.

More fancifully, perhaps, the shuttle can become the critical link in a system that sends astronauts in other kinds of vehicles out to explore the planets. And it is certain to become a major part of the national defense system; the potential of spacecraft or space platforms in maintaining peace or spreading destruction around the world is almost unlimited

If something goes awry in today's test flight or in later tests, all that will have to wait while the engineers go back to the drawing boards. A disaster would mean a postponement, not a cancellation. A space shuttle of some kind -- the Columbia or something else as yet undesigned -- is the key to any program that fulfills, someday, the ultimate promise of space flight.