At the start of the Reagan administration, the trendy word when it came to the economy was "noise." It was used within a then-optimistic White House to describe the anti-inflationary psychology the president would generate by cutting both the budget and the role of the federal government. Now, though, there is a new "noise" coming from the White House. It is the sound of an administration coming apart.

The first clear sign of that, in this administration or any other, is the leaks coming from the White House. Maybe White House staffers are trying to establish a record that they are not responsible for the present economic debacle or the worse one they fear might be coming.

But the second--and more important--reason is that leaking is about the only way the staff can communicate its views and fears to the president. He might not want to listen to them, but he sure reads the papers. Page One has become the memo of last resort.

The White House now has a new edict against leaks. Presidential aides now have to get permission before talking to the press and White House telephone logs have been reviewed to see who is talking to whom. If experience is any guide, none of the leakers will be caught and the leaks will continue.

The leak seems the only way to reach this president. Time magazine recently reported that when White House chief of staff James Baker III at one point broached the idea of a tax increase coupled with a defense cut, the president responded, "If that's what you believe, then what in the hell are you doing here?" As a question for Baker, it is not a bad one, but as a way of furthering a discussion it is not quite the Socratic method.

In fact, if you have been a careful (or even casual) reader of the press, you will already know that the president is disengaged (Newsweek), that his staff is afraid of bringing him the bad news (Time), that it has conspired to have certain key senators educate him on the state of the economy (The Washington Post), that some staffers opposed basic parts of the economic program almost from the start (The New York Times) and that they are now almost united in trying to get the president to face up to reality (The Wall Street Journal).

The upshot is a portrait of a president who has excused himself from the process of governing. The last-minute agony over the fiscal 1984 budget is an example of that. As late as last summer, the White House had projections that the budget could wind up as much as $200 billion in the red.

It feared, as economists and business leaders now do, that such a deficit not only would signal that the president had lost control of the budget process, but that it would again drive up interest rates--dashing any hope for a sustained recovery. Yet from all reports the deficit total came as a complete surprise to the president.

All this has produced "noise"--the psychology that the administration is adrift because the president is out of touch. If the administration was originally right about the utility of "noise"--and it was--it cannot now dismiss it.

The impression that the president is doing nothing is as important as the impression that he is doing something. Only the president, not his staff and not any attempt to curtail leaks, can correct that impression.

But this president remains aloof--a newsreel version of the presidency. He leaves not just the details, but the presidency as well, to others, choosing to enunciate bromides when real solutions are needed. He prefers a false harmony to a heated discourse that just might tear him from views that are, it seems, his political security blanket. On a daily basis, he plays at being president.

Democrats might take some cheer in all this and journalists, for whom bad news is good for business, might relish it, but the fact is that the stakes are greater than partisan advantage or tomorrow's front page.

The actual drift has produced an even greater "noise" of drift--a virtual din that only the president can quiet. Ronald Reagan wants to be presidential. It's understandable--and maybe fun. But it's not the same thing as being president.