While professionalism has never been considered one of the higher virtues in this town, it was discouraging to see the cheapening of journalistic values in last week's White House press conference. Reporters demonstrated anew that they are far less interested in meeting their role in a democratic society than they are in performing in a show-business act titled "See How Clever Am I in Skewering the Nation's Top Executive."

The function of the press conference, and of briefings, is to advance the interests of an informed electorate, sometimes, admittedly, by digging hard at reluctant spokesmen. When that purpose is jettisoned in favor of the career interests of someone seeking neither clarity nor information but his moment in the klieg lights, the claim of the press to a privileged position is weakened.

The president's opening on the issue of taxes was obvious, as was his clear unwillingness -- or perhaps inability -- to make a flat-out concession in advance of negotiations with the Hill. What followed was, by and large, not a proper journalistic chase after administration positions on vital issues, but repetitious elbow-to-elbow posturing of a supporting cast trying to crowd out the top banana.

NAT KINGSLEY Chevy Chase