An internal Air Force memo says that the need for more cargo airplanes to haul military equipment to remote world troublespots may be met by Boeing 747s, which the manufacturer estimates would cost at least $6 billion less than the combination of rival aircraft favored by Defense Secretary Caspar W. Weinberger and the Air Force.

The memo, written by the Air Force studies and analysis branch, was requested by Deputy Assistant Secretary L. K. Mosemann II to prepare for a Senate Armed Services Committee hearing this morning.

Last night, an Air Force spokesman had no comment on the analysis made in the memo but said parts of it have been changed and that an official Air Force position had yet to be reached. The memo was prepared by Maj. Thomas Mikolajcik and signed by Brig. Gen. John A. Shaud of the office of the deputy chief of staff for plans and operations.

The Pentagon wants to spend $11.6 billion for 50 more Lockheed C5s and 44 more McDonnell Douglas KC10s to fill strategic airlift requirements. Weinberger decided against buying 747s, telling Sen. Henry M. Jackson (D-Wash.) in a March 1 letter that the Boeing aircraft "just does not have the military utility of the C5."

The studies and analysis branch memo gave good marks to both the 747 and the C5, which carries "outsize" equipment such as artillery, heliocopters and tanks.

The memo said that on the basis of "the Boeing assumptions," the branch "does not dispute the Boeing claim of equality between the DOD program and their the company's alternatives."

Although Boeing assumed that some pieces of outsize gear would be disassembled to be fitted into 747s, this "does not violate any existing Air Force or Army practices," the memo said. "However, while the Army does this today they would prefer not to do it in the future."

On one key point, the time needed to unload cargo on arrival, the 747 and the C5 came out even. Loading a 747 takes "a little more time," but, the memo said, "It should be remembered that . . . these aircraft can carry more cargo" than a C5. As for flight time, the faster 747 was given the edge.

Turning to the C5, the memo said, "The difference between the Boeing proposal and the DOD program lies in the unique military utility and full range of loading flexibility provided by the C5 aircraft. Also, the DOD program addresses the airlift shortfall with a balanced outsize/oversize cargo procurement strategy."

After Weinberger decided against Boeing in January, the company argued that 60 of its 747 freighters would meet the Pentagon's requirements, carry equal tonnage, be in hand at least three years sooner, and save $6.3 billion. The saving would rise by $500 million if surplus 747 commercial airliners were to be bought and modified, the company said.

Boeing said that the present Air Force fleet of 77 C5s is large enough to meet all of the needs of the Rapid Deployment Force for strategic airlift of huge pieces of outsize equipment. The company proposed that the 747s carry mainly oversize cargo such as trucks and bulk items. Lt. Gen. Kelly H. Burke, the Air Force research and development chief, in an interview last Monday, denied that the C5s are adequate for outsize requirements.

The memo was the second Pentagon internal paper in two days to be obtained and released by the Project on Military Procurement, a nonprofit group that monitors military spending.

In the first memo, Army Undersecretary James R. Ambrose wrote Defense Undersecretary Richard D. DeLauer that it was "scandalous" for the Pentagon to buy the C5s and KC10s instead of switching to an all new cargo aircraft.

Today's the Senate Armed Services Committee session will take testimony from high Pentagon, Army, Air Force and Marine Corps officials in an atmosphere that is politically charged. The states of two ranking Democrats on the committee have large economic stakes in the ultimate decision.

Sen. Sam Nunn (D-Ga.) strongly favors the plan: his state would gain an estimated 8,500 jobs if Lockheed Corp. reopens its C5 production line in Marietta after a 10-year shutdown. But a purchase of 747s, favored by Jackson, would be a boon to Washington state, because Boeing builds the planes near Seattle.