President Reagan is finally doing something about what has been the major flaw in his foreign policy apparatus: chaotic organization. The appointment of William Clark to replace Richard Allen as national security adviser augurs well for improving the management of policymaking. Mr. Allen, aside from questions about his moral judgment, was not a good administrator, and the bureaucratic infighting which took place during his tenure adversely affected the conduct of diplomacy. Mr. Clark's task will be to show that the National Security Council can effectively serve the President without the bitter personal conflicts which traditionally seem to dog that institution.
On the face of it, it is strange that the national security post should go to someone so inexperienced in foreign policy. But, by all accounts, Mr. Clark proved himself a good listener and quick learner as deputy secretary of state. In a short year of diplomacy he performed a number of missions abroad and earned the respect of State Department ''pros'' as an effective manager and in-house mediator. Because he has won the confidence of Secretary of State Haig, and because Mr. Clark is thought to be without personal political ambitions, it can be hoped that the two will work together well and that Mr. Haig will be allowed to be the primary formulator and articulator of US foreign policy. Certainly Mr. Clark will want to avoid the troubles which have often beset the US abroad because it spoke with more than one voice.
Most important, of course, is the fact that Mr. William Clark is a close confidant of the President. He will have daily meetings with him and access whenever needed. With his political weight, he will necessarily be in a strong position himself when putting policy options before Mr. Reagan - from State, the Pentagon, the CIA, and other agencies - and when following through on implementation of decisions reached. While the job ostensibly is one of coordination and central control, national security advisers have come to have considerable influence in their own right. However, powerful advisers in the past have had professional and conceptual skills which Mr. Clark does not have, so it remains to be seen if he is up to the potential of the job. It is reassuring at least that Mr. Clark, while conservative, tends like the President to be more pragmatic than ideological in approach.
There already is press speculation about the political implications of Mr. Clark's elevation. The triumvirate at the White House - Meese, Deaver, and Baker - now are joined by a fourth potentially powerful figure. No doubt operations of the inner circle will change to some extent; Mr. Meese after all previously handled the national security briefings of the President. But we would like to think that big power rivalries at the White House are more the musings of the media than objective reality - and that, in any case, the President keeps the competition under control. Mr. Clark put it well when he said: ''It's not a matter of any power. It's a matter of duty as directed by the President.''
That is a splendid guide for any public servant.