The Civil Aeronautics Board has concluded that "there is reason for serious concern over the competitiveness" of the computer reservations systems used by airlines and travel agents, but that more investigation is needed before these concerns can be confirmed or dismissed.

That conclusion came in a two-volume report to Congress the board released last week after a preliminary staff investigation. The central allegation is that the two major computer ticketing systems have been programmed by their owners--United and American airlines--to the disadvantage of other airlines.

Those systems tell travel agents what flights are available between cities, and for what price. The owning airlines admit their systems display their own flights first, if they have flights between the cities requested.

Board Chairman Dan McKinnon said at a closed conference of CAB members last week that Congress should hold hearings before the board decides to take further action.

But Board Member James R. Smith pushed for a full-bore CAB probe to see if the consumer was damaged by the computer bias.

Smith said the CAB should address the question, "Does the consumer have knowledge of the best available fare and the best available service" for any flight? "In all cases," Smith said, "I think the answer to that that we determined is no. Is this anticompetitive? Who knows? . . . Let the Justice Department pass judgment on that . . . Is it against the public interest, however, from a consumer standpooint? And I think the answer to that is yes. It is not in the public interest."

Finally, the board simply forwarded its preliminary findings along with six options that ranged from doing nothing to instituting a formal inquiry of possible unfair practices under the Federal Aviation Act.

At the same time, the Justice Department's antitrust division is continuing its civil investigation into computer reservation systems, according to Elliot Seiden, chief of the division's transportation section.

Complicating the CAB's future role are the facts that Justice already has a full investigation going and that the CAB will go out of business Jan. 1, 1985.

Therefore, any investigation would be limited by time and the enthusiasm of staff members looking for new jobs.