The battle over allocation of foreign-policy powers between the president and Congress, joined so publicly during the Reagan administration, has moved underground amid signs that neither branch learned much from the traumas of the late 1980s.

The Bush administration, bolstered by bold misreadings of the Constitution and its history, has issued sweeping claims of executive power that virtually exclude Congress from the conduct of foreign affairs.

Two administration lawyers recently asserted in a letter to The New York Review of Books that the Framers had intended a system "whereby the president executes the law and conducts foreign affairs, subject only to specific congressional checks"-and armed with ”a residual power that encompasses all authority not expressly delegated to the other branches of government.”

And in a pretrial brief in the Oliver North case, Dick Thornburgh’s Justice Department contended in 1988 that "the president has plenary power which Congress cannot invade" to circumvent congressional spending bans by soliciting money from foreign leaders for covert military operations. When Congress voted last year to bar such solicitations, the administration said it was unconstitutional and the president vetoed the bill.

Meanwhile, after episodic resistance to the Reagan policies in Central America, Congress has resumed its decades-old habit of acquiescence in unilateral presidential actions, including those that skirt its own laws.

When the president invades Panama, hardly bothering to notify (let alone consult) anyone in Congress, the public approves, so Congress applauds. So much for the War Powers Resolution of 1973, which was supposed to prevent unilateral presidential use of military force.

And since Vietnam the courts have largely abdicated their traditional role of policing the boundaries of executive and legislative power over foreign affairs. Instead, they have deferred so broadly to the executive as to call to mind a pronouncement of Richard Nixon’s: "When the president does it, that means that it is not illegal.”

If recent history is any guide, this pattern of unchecked presidential unilateralism will continue until the next disaster or scandal comes along; then Congress will once again swoop down spasmodically to investigate what went wrong and assess blame.

Can the cycle be broken? Is exclusive presidential control of foreign affairs the only way the United States can function as a world power? Can institutional reforms foster real executive-legislative collaboration?

The congressional panels investigating the Iran-Contra affair shed little light on these questions, preoccupied as they were with uncovering facts and fixing responsibility.

But a new book offers thoughtful proposals for reviving the checks and balances designed by the Framers, with the executive and legislative branches sharing foreign-affairs powers and the judiciary umpiring interbranch disputes.

Harold Koh, a Yale law professor and former Justice Department lawyer, shows in The National Security Constitution: Sharing Power After the Iran-Contra Affair that the Constitution and its history confine the sphere of exclusive presidential power to the conduct of diplomatic communications and recognition of governments. All other presidential actions are subject to congressional oversight and disapproval.

In theory, that is. Dissecting the creeping executive hegemony over foreign policy since Vietnam, Koh also explains "why the president almost always seems to win in foreign affairs" in the short run-and why, in the long run, this leads to "a reactive era of presidential defeat," at great cost to the nation.

Iran-Contra was no mere aberration, he shows, but rather an extreme example of the executive hubris that has been fostered by "an uncured constitutional crisis in national security decision-making that awaits to afflict us anew.”

"In the end," Koh says, "that affair should be understood not as a case of bad people violating good laws (as the various investigators concluded), or of good people violating bad laws (as-Oliver North’s supporters maintained), but of seriously misguided people violating seriously ineffective national security laws."

While we cannot legislate executive-branch honesty or congressional courage, we can write better laws. But so far Congress has done little either to avert a recurrence of Iran-Contra or to counter the dispersion of power within Congress itself that impedes constructive foreign-affairs partnership with the executive.

Congress backed down, in the face of veto threats, presidential promises to behave, and political pressure, from requiring that designated congressional leaders be told of covert military actions within a fixed time period.

And despite the Reagan administration’s covert sale of $30 million in missiles to Iran’s terrorist government, there is still no law clearly requiring that anyone in Congress be notified of any similar sales in the future.

Koh’s book records myriad episodes in which executive-branch officials have circumvented, found loopholes in, or simply ignored the patchwork of laws Congress passed after Vietnam to require the president to consult it concerning important actions abroad.

Like many liberal analysts, he identifies the essence of the problem as unhealthy presidential unilateralism in running foreign policy.

But Koh also concedes the necessity for the president to play the "predominant role in making foreign-policy decisions," given the inability of 535 members of Congress to formulate common goals, act quickly, or keep secrets. And he shows how "Congress and the courts too easily . . . avoid constructive participation in important national decisions."

Koh’s overall objective is "to force the president to consult with Congress before he acts, and second, to Force Congress to declare approval or opposition to his action promptly after it happens.

His 50 pages of detailed structural reforms are necessarily complex. The centerpiece would be a comprehensive "national security charter" supplanting the patchwork of existing laws governing use of the military, intelligence agencies, and emergency economic powers, and specifying internal and congressional checks and legal reviews of executive-branch decision-making.

A key mechanism would be a "core consultative group" of congressional leaders equipped with the centralized staff, the legal expertise, and the power to demand whatever sensitive information it needs to render informed judgments, and with the right to be notified and consulted before any use of military force or covert operation.

Congress should also seek to legislate away the various jurisdictional doctrines the courts have used to avoid deciding on the merits the legality of challenged executive-branch actions, Koh argues.

The ineffectiveness of such post-Vietnam legislation as the War Powers Resolution has led to skepticism about the efficacy of any regime of legal restraints on executive autonomy in foreign affairs. Conservatives, wary of hamstringing presidential power, prescribe something approaching presidential autocracy in the entire foreign-policy realm.

We are drifting in that direction. But Koh’s book argues eloquently that the result is not effective policy but the disastrous failure of ill-advised presidential initiatives like Vietnam and Iran-Contra, with recurring cycles of "crippling interbranch strife.”

While his proposals would reduce presidential autonomy, Koh says "the long-term intent is to enhance presidential strength” by preventing presidents from initiating policies that cannot command public support.

In this regard, he reminds us that Justice Robert Jackson’s 1952 concurrence in the steel seizure case provides a measure not only of constitutional legitimacy but also of practical sustainability: "When the president acts pursuant to an express or implied authorization of Congress, his authority is at its maximum, for it includes all that he possesses in his own right plus all that Congress can delegate.”