You can never be sure what's going on around this town sub rosa, but my current nominee for scandal of the year has to be the Reagan administration's management of foreign policy.

"It's a mess," says a career diplomat who is also a presidential appointee with a professional stake in the administration's success. A veteran ambassador to Washington finds the Reagan method the "most disorganized" he has ever seen. This is not exceptional hyperbole: it's the not-so-muffled, common complaint of many responsible participants, one way or another, in the conduct of American diplomacy.

Serious students of past performances argue that the Reagan system bears no resemblance to anything that's gone before. None of the previous models fit: not the Truman confidence in a dominant secretary of state; not the Eisenhower reliance-on-military-staff formula, with a vastly expanded National Security Council apparatus; not Nixon's decision-making in isolation, with Henry Kissinger the key; not Jimmy Carter's nitty-gritty personal involvement.

Reagan has borrowed bits and pieces, to be sure: Cabinet government of a sort; a supposedly dominant secretary of state in Al Haig; central White House oversight, but not in the traditional manner of a traffic-directing special adviser to the president for national security affairs. In that capacity, Richard Allen is a crucial layer below the awesome triumvirate of Jim Baker, Mike Deaver and, above all, White House counselor Ed Meese.

The result is a system, as one critic puts it, that has "almost none of the strengths and most of the weaknesses of everything that's gone before." By which he means too many divergent voices, no "policing" of the execution of decisions presumably made--"a loose cannon on a pitching deck."

The internal costs in carping, sagging morale, debilitating infighting and simple lack of direction are already high and rising. Externally, where the costs are reckoned in the confidence and understanding of allies (and the potential for misunderstanding of adversaries) the costs are higher, more damaging and more dangerous.

Just when you think you have the quintessential illustration at hand, another example crops up: witness Defense Secretary Caspar Weinberger's efforts to tidy up--for the benefit of dismayed and disbelieving Europeans --the president's offhand projection of the possibility of a tactical nuclear war, nicely confined to European battlefields.

Or witness the administration's handling of the AWACS sale to Saudi Arabia. Win or lose, it's a downer to some degree on the competence chart. But a far more telling illustration, and a clear loser on the confidence chart, is the administration's exposition of its security obligations to Saudi Arabia.

The self-proclaimed Carter doctrine, by comparison, was a model of clarity: "Any attempt by any outside force to gain control of the Persian Gulf . . . will be repelled by use of any means necessary, including force." All that was missing, to make it compelling, was the visible availability of the necessary force.

That same deficiency applies as well to the Reagan approach (simple charity demands that it not be elevated to the level of a doctrine). But in Reagan's case, not just the means but the ends are obscure.

First, there was the president's flat declaration that "we will not permit" Saudi Arabia "to be an Iran." Since almost everybody agrees that Iran's shah fell victim to a strictly internal upheaval, this seemed to take the American commitment well beyond a threat from "any outside force."

Next came Weinberger, saying the United States "would not stand by, in the event of Saudi requests, as we did before with Iran, and allow a government that had been totally unfriendly to the United States and the Free World to take over." Positive reinforcement, you could say, of the president.

Comes now, a week later, counselor Meese (not a longtime student of these matters) pooh-poohing the internal/external question on the grounds that, in historical terms, an uprising against the house of Saud "doesn't seem very likely." But wait. That same day, in an effort to clarify, Richard Allen was saying there is "no question" about what the president had in mind: "We are prepared to assist should there be an external attack upon the government of Saudi Arabia or any of the other states in the region."

So we are back to a Carter doctrine for dealing with "outside" attack--I guess. But we are also back to the problem of too many responsible officials saying different things. It might have been understandable, say, six months ago, or even three. What raises it to the level of scandal, of a sort, is not just that it persists--or that it is precisely what Ronald Reagan complained of in the Carter presidency. The worst part of the problem affecting Reagan's foreign policy management is that the only person who can do anything about it, which is to say Ronald Reagan, gives no evidence of even being aware that it exists.