Proponents of legislation to reduce federal airline regulation yesterday exhorted Congress not to view the current spate of discount fares as a substitute for legislation.

Stuart E. Eizenstat assistant to the president for domestic affairs and policy, told an all-day forum on airline regulation that the airlines only began to seek approval to offer discount fares when the prospect of legislative change improved. The administration supported measure is needed to "make pressure for fare cuts permanent and extend it to regular coach passengers" he said.

Eizenstat's remarks were made at an all-day forum sponsored by the Ad Hoc Committee for Airline Regulatory Reform -- a coalition of two dozen "public interest," business governmental, and political groups -- to familiarize House members and staff with the issue of airline regulation. The House Aviation Subcommittee is scheduled to begin marking up a measure on March 1.

Eizenstat said the measure must include a "strong" provision allowing airlines freer entry into new routes, the power to adjust their own fares without government approval, and a subsidy program to assure small communities of air service during the transition period from current regulation to a more competitive environment.

He said he believes there is a broad base of support for this type of legislation because of a growing view that "there is too much government regulation. . .

"What the airlines need to do is to please their customers and not the regulators," he said.

Elizabeth Bailey, a member of the Civil Aeronautics Board, agreed with the need for new legislation. Even the "pro-competitive" board on which she sits cannot do everything it may think is in the public interest under the 1938 law, she maintained. She said lawyers at the board estimate that it will be between three and six years before the courts decide whether some of the changes they are effecting are legal under the statute.

The board is trying to expedite procedures -- by streamlining the mandated hearings -- and to find ways to interpret the statute in the most precompetitive way, Bailey said. Nevertheless, board members are forced to "make choices we shouldn't have to make." As a result, the board considers applications for service to the larger cities because they would yield benefits to more people, she contended. That means not hearing applications for new service to smaller cities she added.

In other presentations:

Transportation Secretary Brock Adams said the current law, which requires the CAB to "promote" as well as regulate the airline industry, puts the CAB in an "impossible" situation.

Mary Schuman, assistant director of the White House Domestic Policy Staff, noted that, even with a board willing to grant authority to new air lines to enter new routes, applications filed in October 1976 for new low-fare service in and out of Chicago's Midway Airport still are tied up in the time-consuming and cumbersome board procedures.