The Air Force has agreed to suspend the bidding on a $3.5 billion computer contract after Digital Equipment Corp. complained that the bidding was stacked in favor of a competitor.

Dozens of companies are bidding for a piece of the contract to provide 20,000 small, multiple-user computers to the Air Force.

"This is a big one," said Frank Donovan of Digital's government systems group. "We're very pleased to have won the time to prove our case."

In a complaint to the General Services Administration's board of appeals, the Maynard, Mass., computer maker had charged that the Air Force's contract requirements amount to an "illegal limitation of competition" because they call for operating-system software developed by competing bidder American Telephone & Telegraph Co.

Officers of the Air Force Computer Acquisition Center could not be reached for comment after the GSA decision. But in a telephone interview last week, Lt. Col. Warren Webber defended the contract's terms. "The Air Force needs standardized computer systems and this is a means to achieve that goal," he said.

Webber called the pending contract "historic" and said it would be among the largest ever undertaken by the Air Force. "This is a major contract and it could lock out the losers from a lot of government business. It's a winner-take-all situation."

Webber said six or eight major computer companies were expected to pursue the contract.

Digital asked the Air Force to revise the pending contract but was turned down July 29. The company appealed the decision, asking that specifications requiring use of AT&T's System V Interface Definition, a variant of AT&T's widely-licensed Unix software, be deleted from the contract.

Digital's Donovan complained that the Air Force should be specifying functionality, not specific software. "The question is whether the Air Force should be asking for bids on a Chevy Chevette, or specifying a four cylinder, two-door automobile."

Contract proposals had been due early next month. Instead, an administrative law judge will consider Digital's complaint in a Washington hearing Sept. 16.

In its initial rejection of Digital's protest, the Air Force said that it had made specifications "as liberal as possible" while maintaining the ability to buy systems "that will not tie us to a specific vendor over the long term."

The pending contract "provides for maximum competition" while meeting the Air Force's minimum needs for widely accepted software standards, the Air Force said