NASA long-term expections drop as Columbia heads skyward again.

Out on Pad A at Launch Complex 39 at Cape Canaveral, Fla., space shuttle Columbia is poised to make history as the first spacecraft ever to be refurbished and returned to orbit.

At this writing, the preliminary countdown was proceeding smoothly toward an anticipated launch at 7:30 a.m. EST, Nov. 4.

Shuttle enthusiasts wish they could be as confident about the longer-range prospects of what the National Aeronautics and Space Administration (NASA) calls the Space Transportation System (STS).

Shrinking budgets, along with the realization that it probably will take a number of years of on-the-job training before efforts to turn the shuttle around between flights move with ''airline precision,'' have curtailed expectations. NASA has cut the shuttle flight schedule for the next four years from 44 to 28 missions. There is speculation it may be reduced even more to meet President Reagan's demand for further spending cuts. Indeed, Mr. Reagan has delayed a statement of support for the shuttle that was expected in September until after the upcoming test flight.

Thus the attitude in the US space community reflects a mixture of short-term optimism and long-term anxiety for the mission of astronauts Joe H. Engle, mission commander, and Richard H. Truly.

At this writing there seems little reason not to be optimistic about Columbia's 5-day, 4-hour, and 10-minute mission. The shuttle team has coped competently with technical difficulties that have at times seemed frustrating to onlookers.

The computer timing glitch April 10 that delayed the first launch by two days was quickly dealt with. And in spite of the lost heat protective tiles that caused so much comment during that first flight, Columbia came back in good condition. ''I wish I could buy a used car that looked as good as this does,'' Captain Truly quipped at the time.

One of the most serious problems of that flight occurred during the first second or so of the launch. Shock-wave pressure generated by the solid fuel booster rockets was four times what had been expected (2.4 pounds per square inch instead of 0.6 p.s.i.). This made the spacecrafts' wing elevons flap and buckled a fuel tank strut near the crew cabin.

Engineers at Cape Canaveral believe they have solved the problem with a system of water troughs made of nylon sailcloth stretched across rope which should disperse the shock wave. Jets spraying some 100,000 gallons of water a minute directly into the rocket plume will also help.

More recently, there was a spill of nitrogen tetroxide oxidizer Sept. 22. The chemical is used with the fuel monomephyl hydrozine in the shuttle orbital control rockets. These are highly reactive chemicals. Fuel and oxidizer ignite on contact. The spill of only two to three gallons of the corrosive oxidizer onto the forward area of the Columbia made it necessary to remove 370 tiles. A pint of it also dampened 26 thermal blankets inside the craft. This postponed a scheduled Oct. 9 launch.

Now the tiles and blankets have been replaced. The oxidizer has been cleansed of the iron nitrate contaminant, whose presence at a concentration of only about five parts per million corroded a valve and caused the spill. And the fuel and oxidizer have been loaded.

Shuttle managers wish the longer term problems could be dealt with as easily. The Space Transportation System is more than just the orbiter shuttle and its external fuel tank and solid rocket boosters. It's a complex of personnel, ground facilities, and logistics whose purpose is to make STS operations run as smoothly as those of an airline, with as little as 12 days between shuttle flights.

NASA is nowhere near having that goal in sight. Even when shuttle crews have abandoned the broad flat land at Edwards Air Base for the narrow landing strip at Cape Canaveral, thus eliminating the delay of ferrying the shuttle across a continent, turnaround will still be far from routine. For all its ability to withstand the vibrations and accelerations of launching and the fiery heat of reentry, the shuttle is a delicate craft. It is easily damaged when knocked by a forklift truck, as happened in preparing Columbia for its second flight. Before shuttle turnarounds are truly ''routine,'' the ground team must go through years of developing procedures, testing them, refining them, and testing again.

Then there are questions of continued funding. Four orbiters are authorized, a fifth, which NASA wants, is uncertain. Production even of the fourth is being stretched out and, as noted, the projected flight schedule has been cut back sharply.

All of this makes prospective commercial users of the shuttle, with such projects as making ultra-pure crystals for electronics, unsure when or whether to commit their own funds.

Richard Brown of the Marshall Space Flight Center in Huntsville, Ala., who is soliciting such customers, admits this makes ''a risk factor for businessmen'' that dampens their enthusiasm. NASA administrator James Beggs also acknowledges the problem but says bravely, ''This is no different from starting up any other business . . . . ''

Thus, in spite of the precedent Columbia is expected to set as the first used spacecraft in orbit, this will only be one small step toward a goal more demanding than putting men on the moon - the goal of making manned space flights a routine commercial, as well as military or research, operation.