Here we go again with yet another effort to exorcise the bane of every American president's existence: the leaking of classified "national security" information. The Reagan administration is applying what you might call the Samuel Johnson Doctrine on Hanging.

"When a man knows he is to be hanged in a fortnight," Johnson said, "it concentrates the mind wonderfully." The Reagan administration apparently thinks that the same may be said of the imminent prospect of being strapped to a lie detector, currently the instrument of choice in the investigation of security breaches. Officials handling National Security Council documents henceforth must sign an attached cover sheet acknowledging their responsibilities "under the law" and pledging to "cooperate fully" with any "lawful" investigation.

The best that can be said of this approach is that it is a vast improvement over an earlier order promulgated by the president's new national security adviser, Judge William Clark, which would have required advance top-level approval for most officials even to talk to reporters about classified matters. But anybody who has been in the thick of the national security business will tell you 1)that almost every conceivable variation on the Clark approach (including lie detectors, not to mention the Nixon wiretapping) has been tried before and 2)that even unacceptably Draconian measures do not work for long, if they work at all.

This is not to say that the government can't successfully keep vital secrets by strictly limiting access (the Nixon opening to China is a case in point), or that it doesn't have every right to hold back sensitive information. The point is that restricted access to, and policing of, the favored few can be as injurious to healthy policy-making as the occasional gross violation of security.

What's more, strict security measures do not necessarily get at the likely sources of the trouble, which have much less to do with slack enforcement than with raging, unresolved policy disputes, low morale, personality conflicts, territorial imperatives and the frustrations of a harshly competitive policy-making process.

The Reagan administration is afflicted with more than the usual amount of this sort of bureaucratic ferment and conflict. Perhaps that's because it is shot through with undisciplined ideologues, fierce in their devotion to the "mandate" they believe their man received: to enact just about every ill-considered, unrealistic notion that found its way into a presidential campaign speech or the Republican Party platform.

Whatever the case, the internal guerrilla warfare--the White House against State, State against Defense--is fought by leaks. Sometimes the leakers leak their own point of view. Sometimes they leak the prevailing view of their opponents (in the worst possible light).

It is not too much to suspect that this sort of infighting was at work in two leaks that are supposed to have contributed to the crackdown: one involving suspicious crates of what were thought to be Soviet military aircraft in Cuba, and the other revealing details of the administration plan to sell Taiwan a less-fancy fighter plane than the Taiwanese wanted.

In the first instance, you could assume a desire to whip up sentiment for a tougher line on Cuba; in the latter, a desire to fan opposition to the Reagan China policy. Can the new rules restrain this sort of thing? Perhaps, by the most stringent limits on the distribution of classified information and by narrowly confining the decision-making process to a select few.

But the government is big; its workings involve large numbers of people. Foreign policy, be it Poland or El Salvador, cuts across State, Defense, CIA, Commerce, Treasury--not to mention allied governments. Bureaucrats talk-- to each other. Leaks do not ordinarily take the form of entire documents; they are assembled from bits and pieces, some innocuous, some sensitive.

Lyndon Johnson's celebrated, cozy Tuesday luncheons--the forum for Vietnam policy-making--are testimony to the danger of circling the wagons too tightly. The resulting leaks, some less reliable than others, were part of the price. A tight lid doesn't necessarily reduce the pressure from the warring factions down the line to force out their side of the argument.

The Reagan administration promises to balance security against the public's "right to know." But a proper balance has to include what the decision-makers themselves need to know --and may be shut off from by tight security. History suggests that it has never been an easy balance to strike.