Amid all the furor over at the Corporation for Public Broadcasting last week, it was never entirely clear why the White House, at the last minute before the CPB board held its annual meeting to elect officers, tried to push through a new "recess appointee" to be seated without the advice and consent of the Senate because Congress was out of session. The effort failed, at least for the time being, after the board simply voted not to seat the appointee, William Lee Hanley Jr. Some Democrats on the board immediately jumped to the conclusion that the unusual appointment was made because CPB Vice Chairman Sonia Landau, a Republican, needed that extra vote to be reelected vice chairman. But now that the dust has settled, it appears that may not be the answer. Sources at CPB say Landau in fact already had the votes to be reelected and was blindsided by the recess appointment, which upset many board members by its indelicacy and cost Landau her vice chairmanship. Because the whole business was so messy, CPB chairman Sharon Percy Rockefeller and other Democrats on the board decided to leave the post vacant rather than press their advantage last week to elect a Democrat as vice chairman in Landau's place. Why did the White House do it? The answer may be simply that, having failed last spring to get Senate confirmation of one of its appointees, Helen Marie Taylor, the White House decided to go ahead with a recess appointment without calculating the fine points of its political impact at CPB--damn the torpedos. In any case, all this will soon be academic. The Reagan administration has two seats to fill on the CPB board--conservative radio broadcaster Paul Harvey may be the other appointee--and, if the rivers don't rise, there will soon be a Republican majority there for the first time in years.