Lockheed Corp. is likely to exceed the maximum amount allowed in its contract for building 50 C5B transports by $566 million, according to an Air Force memo that came to light yesterday.

In making the memo public, the watchdog group Project on Military Procurement warned against attempts by Lockheed to make up for this "overrun" by charging the money to changes the Air Force is likely to request as the plane moves along in production. An Air Force spokesman said last night that the service is determined to keep that from happening.

The memo was written by LeRoy T. Baseman, chairman of an Air Force cost analysis group that reviewed the 1982 fixed-price contract for the 50 C5Bs. The group estimated that Lockheed's cost would turn out to be $9.1 billion for the 50 planes, or $566 million more than the maximum allowed under the contract, counting escalation clauses.

"This means that Lockheed may realize only about half of their expected profit," Baseman's memo said. He warned that "every change to the contract, which was proposed under conditions favorable to the Air Force, would give the contractor the opportunity to renegotiate the contract value under conditions less favorable to the Air Force. It is suggested that the C5B program be baselined and that engineering changes and scheduled perturbations be kept to an absolute minimum . . . . " $556 Million Cost Overrun Predicted on C5B Contract

Lockheed Corp. is likely to exceed the maximum amount allowed in its contract for building 50 C5B transports by $566 million, according to an Air Force memo that came to light yesterday.

In making the memo public, the watchdog group Project on Military Procurement warned against attempts by Lockheed to make up for this "overrun" by charging the money to changes the Air Force is likely to request as the plane moves along in production. An Air Force spokesman said last night that the service is determined to keep that from happening.

The memo was written by LeRoy T. Baseman, chairman of an Air Force cost analysis group that reviewed the 1982 fixed-price contract for the 50 C5Bs. The group estimated that Lockheed's cost would turn out to be $9.1 billion for the 50 planes, or $566 million more than the maximum allowed under the contract, counting escalation clauses.

"This means that Lockheed may realize only about half of their expected profit," Baseman's memo said. He warned that "every change to the contract, which was proposed under conditions favorable to the Air Force, would give the contractor the opportunity to renegotiate the contract value under conditions less favorable to the Air Force. It is suggested that the C5B program be baselined and that engineering changes and scheduled perturbations be kept to an absolute minimum . . . . "