THE REAGAN administration has worked its way to a fair resolution of the ticklish question of how to deal with national security leaks. Not that it was easy. The president's national security adviser, William P. Clark, had prepared last month a truly horrendous proposal that would have required journalists to obtain advance approval, each time, for "all contacts" below the deputy secretary level.

You don't have to be a journalist to recoil from that idea. It would have gone far to destroy the atmosphere in which reporters and editors can seek facts and insight from officials, and in which officials seek to have information and policy transmitted to the public. This exchange cannot succeed, from either point of view, when it is subject to such organization and monitoring. Fortunately, the administration listened to complaints about the proposal, from some of its own officials as well as from press people, and threw it out.

If leaks are to be plugged, it must be at the source end. This is the broad principle the administration has now adopted. It will be more selective about granting access to sensitive documents, and it will require officials with access to acknowledge by their signature, on each document, their readiness to limit disclosure and to "cooperate fully with any lawful investigation" into leaks. There is always the danger of over-classification. The administration cannot be faulted, however, for asserting a claim to stop leaks of legitimate national security information, so long as it goes about it in the right way.

There is an international angle. At any given moment, a dozen governments are looking for ways to put new limits on the free flow of news; at this moment, for instance, South Africa, which already controls its black journalists, is contemplating the licensing of its white journalists, plus foreign correspondents. At any given moment, again, UNESCO is either just starting or just finishing a conference to assist, develop, protect or professionalize journalists--its virtuosity in finding euphemisms for censorship and state control is unending.

This is the ever-present backdrop to efforts by any American administration to cope with its frustrations over leaks. Any step that has the aspect of harassment contributes to that stream of news distortion and manipulation that is already flowing strong abroad. That is another good reason to salute the Reagan administration for deciding to play it straight.