The Civil Aeronautics Board decided yesterday to attempt to guarantee consumers a reasonable shot at finding the most convenient flight or the best fare when they call a computer-equipped travel agent.

In a unanimous decision that followed lines suggested by the House Public Works aviation subcommittee, the board ordered its staff to draft proposed federal regulations that would dictate fairness standards for computer reservation systems.

Those systems are now used by about 80 percent of all travel agents. The fairness question arises because 80 percent of the computerized agents use systems sold or leased by either American Airlines or United Airlines.

Other airlines have alleged in congressional hearings and CAB filings that American and United, dominant in domestic aviation, use the computer systems to manipulate schedule and fare information in a way that discriminates against competitive flights.

CAB Chairman Dan McKinnon said in an interview that "this is the single most significant factor affecting competition in the airline industry today." Virtually every small airline, he said, perceives "that there must be a balance so they have the opportunity to compete. They're not asking for special treatment, just equal treatment. On the other hand, both American and United have a right to a fair return on their investment" in developing the system.

The board will receive a draft within three weeks, publish it, receive comments and probably hold oral arguments, McKinnon said. Another draft will be published before the final regulations are released, which McKinnon estimated will be in January or February.

American and United declined to comment until they have seen the draft. Both airlines have said that there is bias in their computer systems, but that the bias is not anticompetitive. The Justice Department is also investigating to see if there are antitrust questions.