Members of a presidential study commission on antitrust unanimously endorsed legislation yesterday that would force federal regulatory agencies to give greater weight to competitive considerations in their decision-making.

The commission said enactment of legislation "along the lines" of a bill promoted for several years by Sen. Edward M. Kennedy (D-Mass.) would make agencies focus on the economic effects of their actions and maximize the use of competition as a tool of regulation.

The Competition Improvements Act, sponsored by Kennedy, chairman of the Senate antitrust and monopoly subcommittee and a member of the commission, would prohibit agencies from taking actions that may have anticompetitive effects unless they found:

The action was necessary to accomplish an overriding statutory purpose.

The benefits to the general public clearly outweigh the anticompetitive effect of the action.

The proposed action is the least anticompetitive option available that could accomplish the stated regulatory objective.

A law embodying these concepts "would help tip the balance of agency decision-making in favor of competition," the commission said in adopting a chapter in its forthcoming report to President Carter and to Congress.

Commission members, on a 13-3 vote, declined to exempt health and safety regulatory agencies from coverage of the proposed legislation. One of the three votes in favor of exempting those agencies was Alfred Dougherty, director of the Federal Trade Commission's Bureau of Competition, who was sitting in for FTC Chairman Michael Pertschuk.

The commission report does note, however, that the bias in favor of competition created by the legislation does not go so far as to force an agency to abandon considerations not directly related to competition, such as the adequacy of health and safety standards.

But it notes that as a practical matter, the application of the measure would reduce the probability that agencies would adopt certain anticompetitive actions except in the "rare instances" in which reliance on more competitive approaches truly would frustrate essential statutory objectives.

Commission members agreed to mention in their report the concerns raised by some of them that the legislation should not bar agencies from taking actions needed to provide emergency relief and should not cause undue delay in proceedings.

The presidentially appointed commission in scheduled to meet again Dec. 18 to approve its final report. The panel was appointed in May to study and make recommendations on ways to expedite complex antitrust cases and to consider whether current antitrust immunities and exemptions are justified.