Who is going to run the Reagan administration? The president, of course -- who else? Whether he works only 9 to 5 or, like Jimmy Carter, 5 to 9, weekends included, a chief executive needs "sub-presidents" to decide the many domestic policy issues that fit the portfolio of no single Cabinet department. The president should create his sub-presidents along the natural fault lines of power and prestige in the executive branch:

The Treasury secretary . He is the only logical candidate to head up economic policy. In most countries, it is the finance minister who makes and explains economic policy, short of the head of government. The U.S. Treasury secretary faces obstacles in playing a like role: he has no control over the central bank; the executive office long ago undercut his authority over the budget (OMB) and economic analysis (CEA); and the White House usually insists on dividing the universe into domestic affairs (Martin Anderson) and foreign affairs (Richard Allen), casting economic policy into institutional limbo. By consequence, the rest of the Cabinet finds it devilishly easy to elude general economic discipline.

The president should act as if he had a genuine ministry of finance, allowing the Treasury secretary to dominate economic policymaking and fuse the staffs at Treasury, CEA and OMB to impose economic discipline on the rest of the Cabinet. To seal the bargain, the Treasury secretary should have a White House office, with a staff coordinator to broker the economic agencies and to protect a clear economic channel to the president.

The OMB director. Until 1970, most interagency disputes about programs got settled by the old budget bureau. Only very big or very sensitive isues got skimmed off for special handling by the White House domestic adviser and this tiny staff. But this system has been scrambled by recent administrations. The domestic adviser has acquired (as have the new executiveoffice's staffs -- the Council on Environmental Quality, the Office of Science and Technology Policy, etc.) a large coterie of "isues experts," who compete with the budget examiners on programs.

The solution is to bring back the Good Old Days. Make the OMB director the sub-president for most interagency program disputes. His regular duties in nailing together the annual budget give him the bureaucratic clout and professional staff needed for this added role. Let the rest of the executive office, and the contending departments, busy themselves lobbying the OMI director.

The domestic affairs adviser . The domestic policy staff should shrink, and it should handle only very major policy innovations, important personally to the president. Even these issues will carry a residue of disputation needing a sub-presidednt. The domestic adviser -- enjoying a special intimacy with his chief -- should make those calls.

the chief of staff . Someone has to referee this whole system on a day-to-day basis: steer issues among the sub-presidents, keep policy and politics together, balance central direction against departmental autonomy, impose a schedule and strategy in the process, put down mutinies and arbitrate grievances. No president should waste time on such chores. He needs a true deputy for the task. Last summer, in Detroit, Mr. Reagan considered giving the job to Gerald Ford. More recently, Mr. Reagan has divided the job between Edwin Meese and James Baker. Fron experience in a recent administration, we have no hesitation in saying that two deputy presidents are better than none. Only time and testing will show whether two are better than one.