President Reagan's press conference last Wednesday night was easily the least impressive of his presidency. Reagan had to ask Andy Glass of the Cox newspapers to repeat and rephrase a question the president had not understood while he was "trying to switch gears." At another point the president seemed to lose his train of thought and then haltingly explain: "I thought I had another line there for a minute that I was going to use, but maybe it's just as well that I don't use it." And the questions were mostly not about the improving economy, but rather about the deteriorating affair of the "pilfered" briefing books.

Pilfered is a word that was introduced into the present argument by budget director David Stockman, who may be suffering from terminal arrogance. On Oct. 28, 1980, the day of the Reagan-Carter debates, then-Rep. Stockman told an Optimist Club luncheon in Casopolis, Mich., according to the reporter who was there and wrote the story, almost "word for word" what the candidates would say that night. While even House Speaker Tip O'Neill doubts that the debate was critical to Reagan's getting his present job, it could be said that Stockman--by his impressive impersonation of John Anderson and Jimmy Carter--got his present job through the debates. It may soon be time for a second Stockman trip to the president's woodshed.

Trying mightily to elevate partisan political advantage to high constitutional principle is the mission of Rep. Tony Coelho (D-Calif.), the chairman of the House Democratic Campaign Committee. Coelho points out that all the debate handlers who allegedly had anything to do with the pilfered documents are within a $2 cab ride of the Oval Office. The president could, in Coelho's words, clean up the whole matter "in 15 minutes in his office" by holding a full and frank discussion with his senior people.

One of the characteristics of the Reagan administration--the president's willingness and ability to delegate authority--has almost surely damaged the White House's ability to respond to the continuing revelations. The very same people who are advising the president on tactics are themselves the subjects of the inquiry. Divided loyalties would be understandable and could explain why the president looked so nervous and sounded so unresponsive to questions about the Carter papers at his press conference Wednesday.

As daily disclosures vex the administration, hints are dropped from within the White House about just which body or bodies might be available for dropping overboard for the purpose of load-lightening.

The irony of the president's political predicament remains that the only sound counsel that Ronald Reagan is perhaps currently in receipt of came from a California political adversary, Coelho--"to come clean, now." Another week like the past one and the call will be for a special prosecutor.