Over the vigorous opposition of the Pentagon, a congressional committee today is expected to cancel a proposed computer contract for the Air Force that investigators for the General Accounting Office estimated could waste up to $1 billion.

The Air Force wants to install two sets of computers at 105 air bases around the country, with the identical backup being used if the original computer broke down, in a $5 billion project that would be the costliest computer contract ever awarded by the federal government.

The two-for-one computer idea was first criticized in an internal Air Force audit, which recommended that the project be killed, but that suggestion was ignored and the auditor who prepared the report was shipped off to Korea.

But last month, the Gao issued a blistering report on the scheme, telling Rep. Jack Brooks (D-Tex.), chairman of the House Government Operations Committee, that a single computer system, capable of meeting all needs of the Air Force, could be purchased "off the shelf" at a savings of $600 million to $1 billion over the 20-year life of the contract.

Yesterday, Brooks' subcommittee on legislation and national security approved a report that calls for cancellation of the contract, scheduled to go into effect next March. The full Government Operations Committee will vote on the report this morning.

The Air Force contends that the two-computer idea would not double the cost, as critics suggest. Air Force Secretary Hans Mark, testifying before Brooks' committee on Oct. 10, said, "I find it hard to believe that the savings quoted [IN THE GAO study] are that large."

Brooks responded, "if they are wrong on the $600 million by 50 percent, it is still $300 million [savings]."

Rep. Frank Horton (R-N.Y), the committee's ranking minority member, told Marks "you can justify the redundancy if you are putting a man on the moon, or building a nuclear plant" but not for routine operation of the Air Force.

"We want the system to be available at all times," answered Marks.

John A. Hewitt Jr., the Air Force's assistant secretary for financial management, estimated the dual computer system would cost only 3 percent more than a single one. He said the GAO and the Air Force's own audit agency overestimated the manpower savings if only one computer was used at each air base.

Stopping the procurement process is a "drastic step" that Horton said will cost money also, but will "ultimately result in a tremendous saying." He said the General Services Administration should be able to prepare specifications for a single computer system within six to 12 months "that will save hundreds of millions of dollars."

Despite signals last summer that Congress was unhappy with the two-computer idea, and might kill the project, the Air Force, with the sanction of the GSA, went ahead with the procurement process, looking forward to a contract award next March.

Brig. Gen. Robert E. Chapman, director of computer resources for the Air Force, told the GSA on Nov. 5 that prospective bidders would be advised that the GSA had suspended the Air Force's authority to let the contract, but "oral negotiations between the government actions prior to contract award will not be affected . . ."