During the past nine years we have appropriated more than $7 billion for a new Air Force cargo aircraft -- the C-17. With our airlift force now taxed to the limit deploying U.S. forces to Saudi Arabia, what have we gotten for our $7 billion? Nothing. The first C-17 has yet to lift off a runaway.

Could we have done better? You bet. For what we've already spent on the C-17, we could have bought roughly 70 C-5s, an aircraft of proven design. We already have 126 of them, and though dating back to 1968, the C-5 still carries more and goes farther than the C-17 will but costs about half as much. What's going on here?

Our need for more airlift exploded with then president Carter's characterization of access to Persian Gulf oil as a vital national interest. Building more C-5s would have been the simplest solution, but there was some chance that a new design with the latest technology could overcome the C-5's advantages of no technological risk, no development cost, cheaper production, earlier availability, an existing support system and (as it turned out) better range and payload. So a design competition for a new aircraft was announced to resolve the issue.

The Air Force, intent on a new design, didn't wait for the answer. Before the competition even began, they were lobbying Capitol Hill for the new aircraft, later named the C-17. Although in the '60s they had lobbied for the C-5 on grounds that its ''short-field takeoff and landing ability will enable {it} to operate into short ... semi-prepared airstrips,'' in the '70s they claimed that the C-5 needed long runaways and could use only the largest bases, while the C-17's short-field capability would open up five times as many bases.

Though many fell for it, the assertion was specious. The C-5 was designed with a special soft-field 28-wheel landing gear, which lets it operate where no C-17 will dare to taxi. And a careful look at the ''analysis'' showed that the Air Force had inflated the numbers by counting every jungle airstrip in South America and Africa as equal in importance to the critical bases in Europe and the Middle East.

Not satisfied to leave it at that, Air Force officials also credited the paper C-17 design with a sky-high utilization rate, discounting the C-5's maximum payload that they themselves had demonstrated in flight tests. They also ignored the C-5's three-year earlier availability. (C-5s could be flying to Saudi Arabia today.)

They also boosted the C-5's cost $13 billion by claiming that they would have to buy an extra 180 C-130s (smaller tactical airlifters) expressly to take the C-5's cargo forward from its big air bases to the C-17's small bases, where it would be needed.

That claim was also specious. Even if the C-5 were restricted to large bases (which it isn't), the average distance to the forward bases -- less than 70 miles in the Middle East and 50 in Europe -- is too short for air transshipment. And even if it weren't, the C-5s ''outsize'' cargo (e.g. tanks) won't fit inside a C-130.

To its credit, the Reagan administration crammed an extra 50 C-5s down the Air Force's throat before going ahead with the C-17. But once projects as large as the C-17 -- opening at $37.5 billion -- get started, they're hard to stop.

The Air Force wanted a high-tech aircraft. The Army and the Marines -- desperate for lift -- were happy to endorse a C-anything if the Air Force would only buy it. And the many contractors and subcontractors all joined with their members of Congress in happy chorus. That is, all but the C-5's builder, who was given to understand that lobbying against the the C-17 could be bad for future business.

The fancy new C-17 is overweight and behind schedule. Some think it's still not too late to kill it and resume C-5 production. But it is too late to ease our overburdened air bridge to Saudi Arabia with those 70 C-5s we could have had.

The writer, an assistant secretary of defense from 1977 to 1981, was special counselor to the House Armed Services Committee from 1985 to 1989.