The Army's second-highest civilian, in an internal memo, has described as "scandalous" a Pentagon decision to keep buying Lockheed C5s rather than shift to a new kind of transport plane for shipping military equipment to world trouble spots.

The Pentagon for months has been split over the important and costly question of what kind of long-distance transport planes it should buy for its Rapid Deployment Force and other units.

The Air Force, along with the Army and Marine Corps, initially recommended buying the McDonnell Douglas C17, still on the drawing board, as the airlift plane of the future. It was to be smaller and more agile than the C5 and thus could land close to the battle area.

Defense Secretary Caspar W. Weinberger finally decided to buy 50 more C5s instead.

Deputy Defense Secretary Frank C. Carlucci said in an interview last month that the decision boiled down to a "a proven design vs. a paper airplane." He added that Air Force leaders, once briefed "on the facts as we have them, came back unanimously" in favor of buying the C5.

But in a memo dated Feb. 19 to the Pentagon's chief of research, Richard D. DeLauer, Army Undersecretary James R. Ambrose said the Weinberger decision means "perpetuating a scandalous situation."

The memo was obtained by the nonprofit organization, Project on Military Procurement.

"Surely," Ambrose wrote DeLauer, "you do not expect support for this decision to consist of anything beyond agreeing: (1) Office of the Secretary of Defense has the right to decide; (2) the decision, to which we were not a party, evidently was made in favor of near term long-haul airlift which, of course, is an urgent need. Intratheater requirements, which are also urgent, remain to be satisfied."

Ambrose in his memo characterized a presentation to Congress by Alton G. Keel, Air Force assistant secretary for research and development, on the C17 transport plane as "appalling."

The Army executive said the Keel presentation was "one more illustration of the likely and unreasonable fate of adequate airlift in the hands of an Air Force which has its hands full" with other programs like the MX missile and satellites.

Army and Marine leaders long have complained that they have received short shrift when it comes to setting aside money for the planes and ships needed to take troops and weaponry from the United States to hot spots up to 10,000 miles away.

A segment of the Air Force also has protested over the years that long distance transport planes, the ones that provide airlift, have been passed over in favor of fighters and bombers when it comes to dividing up the budget.

The military's main complaint against the C5, even one with stronger wings, is that it cannot get close enough to the action, partly because the Air Force does not want to risk losing it and partly because planners prefer to use a giant airport as the landing spot.

Critics also contend that the Army and Air Force have failed to coordinate design efforts to make sure weaponry will fit inside available transport planes.

"I continue to believe," Ambrose continued in his memo, "and indeed with increasing strength, that the deployment situation for ground forces will not be straightened out until control of its destiny is given to the using service. To abdicate it in this way to such obvious and long enduring prioritization at the bottom of the list is perpetuating a scandalous situation . . . . Much the same comments can be made about close air support."

Lt. Gen. Kelly H. Burke, Air Force research director, told The Washington Post that the C17 is a better airlift plane than the C5, particularly for landing on rough fields.

But he added that he favored buying the C5 under the generous funding offered by Carlucci because it would save four years in making additions to today's airlift fleet.

In another internal Pentagon memo, William H. Taft IV, Defense Department general counsel, warned on Dec. 11 that buying the C5 after the C17 had won the airlift design competition might bring legal challenges from aircraft manufacturers.