Incoherence in the Reagan administration's foreign policy is not the work of a mischievous media. It's real. Too many people in too many places are putting out too many different lines. There's a lack of discipline.

And only the president can do the needed tightening-up.

That's not just the opinion of a good number of seasoned foreign diplomats in this town, and a host of other observers as well. It is the considered view of the secretary of state, as expressed in an on-the-record interview dealing in part with the making of the administration's foreign policy.

Al Haig groans, amiably, when the subject is raised of his dealings with the White House and the secretary of defense, his relations with the president, the role of Congress and all the rest.

"Growing pains," he explains. "It would be unusual for growing pains to be over in just eight months."

But when pressed for particulars, he is alternately assertive, defensive, philosophical, professorial--and impatient. Unspoken, but implicit, is a suggestion that only Al Haig, the former White House chief of staff and supreme allied commander, has been here before; that he is the only old pro; that his experience and, yes, intellectual superiority in these matters are not matched by his colleagues'--or adequately reflected in his authority.

"Look, God, this is what I've been doing for 20 years," he explains. "Secretaries of defense have a certain set of responsibilities that give them a different set of perceptions. Secretaries of state have the same. I can remember bloody rows between (former defense secretary) Bob McNamara and (former secretary of state) Dean Rusk-- bloody!"

He is not beset, then, with the vicissitudes of vicarship? Only by the widespread exaggeration of what he had in mind when he first described his concept of the vicar's role of a secretary of state at his confirmation hearings, he replies. Conceding that it was, in hindsight, a term better not used, he had "presumed (his) audience had studied national security organization maybe to the extent I have."

Haig's readings have carried him through "volumes" of testimony given in hearings, over a period of three years in the early 1960s, by a Senate committee studying the foreign policy-making process. It was there he found the vicar concept first expressed by Paul Nitze, former deputy secretary of defense and State Department Policy Planning Council chairman, who defined it as the president's "chief lieutenant."

Haig is confident he enjoys that role: "I don't feel deprived of my ability to influence the conduct of foreign policy, not at all." But the perception persists, he agrees, of a lack of central control to deal with, for example, seemingly contradictory statements by Defense Secretary Caspar Weinberger.

"If you're asking me would I like to see greater discipline in that regard, my answer is, yes. But I don't focus it on Cap Weinberger. I focus it on the cacophony of voices."

Q: "In the White House?"

A: "Throughout the administration. I think we have to tighten up."

Q: "Who has to tighten up?"

A: "Well, I think the president."

On the contribution of the press to this cacophony, Haig is emphatic: "Oh, Lord, the press never generates (it). The press reports what it is given."

Is institutional reform needed to strengthen the president's hand--for example a stronger role of the national security adviser, Richard Allen, in the White House? Not in Haig's view. The best system is the system that works best for the president, he believes from his studies of past arrangements.

If the executive branch is in need of tightening up, what of the problems Congress presents in conducting policy coherently? Haig's short answer is that he is all for positive reinforcement, but against such constraints as the Clark Amendment ("ludicrous"), which restricts covert American activity in Angola. "This reduces "diplomatic flexibility"--even though, he hastens to add, he doesn't think covert operations "are in the cards or on our menu."

He accepts Congress' constitutional prerogative to veto transactions like the AWACS sale to Saudi Arabia, as a "safeguard," but would nonetheless regard an adverse vote as "unwarranted interference in the power of the executive."

On balance and in short, Al Haig feels "very comfortable" in his own role. It's the rest of the team, he seems to be saying, that needs to be shaped up--by the president.