The Civil Aeronautics Board yesterday approved by a 3-2 vote a new code of conduct for its members and employees.

The new standards outlining employee responsibilities and ethical standards are less stringent than those proposed in January but are significantly more restrictive than the decade-old rules they will replace.

CAB general counsel James C. Schultz explained to board members at its open meeting yesterday that the original proposals were modified to accomodate several changes suggested by staff and others through the comment process and a public hearing.

For instance, one such change would allow CAB employees to accept invitations to widely-attended functions like Aero Club luncheons. The earlier proposal would have prohibited an employee from accepting any free lunch unless a speaker or participant in a program or in the course of out-of-town travel under certain defined circumstances. The new rules adopted yesterday, however, prohibit what Schultz called "one-to-one tete-a-tetes with interested parties."

New conflict-of-interest standards for board officials and staff was one of the items chairman John E. Robson had hoped to accomplish while he was at the board, and he had instituted a review of the board's existing rules in the summer of 1975. Yesterday was his last official open meeting before his resignation takes effect April 30.

R. Tenney Johnson noted that the new rules respond to a report by the Government Accounting Office which criticized the board for certain procedural. The study the CAB instituted found that some employees didn't know the rules at all. "Some thought they should be permitted to own airline stock . . . own stock of the very companies their agency is regulating.

"You can endlessly go through this rigamarole and say that because every single person at the board hasn't had the last word, we can't act," he complained when Minetti waved the complaint he had received from a staff member and urged delay. "I think for us to sit around and do nothing . . . when we have a feeling about what is right . . . would be unwarranted.

"The whole purpose of these rules is protection of the board's integrity and maintenance of public confidence in the board's integrity," he said.

Robson agreed, "These rules aren't immutable . . . but it strikes me that it is appropriate that the agency speaks at the moment about what the board rules ought to be."

Under the new rules, employees, their spouses and minor children would be prohibited from holding any financial interest in "civil aeronautics enterprises." Under a procedure set up by the new rules, an employee could file for a waiver to allow holdings in a civil aeronautics enterprise, but any waivers granted will be made public.