Requisites for a bipartisan foreign policy

President Reagan's call for a return to the ''tradition of partisan politics stopping at the water's edge'' has a familiar ring. Many of his predecessors have made the same appeal in response to criticism of their handling of foreign policy.

Of course, he is right about the need for bipartisan support from Congress and the public. There is no way to carry on an effective foreign policy without it. It existed most solidly in the first two decades after World War II, but that did not rule out bitter disputes about China, Korea, and defense strategy. Then the consensus was shattered by Vietnam, the illusory Nixon detente, and distrust of the executive.

By 1980, the receding of Vietnam and the reaction to Soviet behavior seemed to offer a chance to revive a consensus among moderates of both parties. Achieving it depended on leadership by the President; Congress could not take the lead. But consensus could not be had merely for the asking. The President had to develop and nurture it by satisfying specific conditions:

* By setting out clear objectives and means for pursuing them which would rally centrist support.

* By inspiring confidence in his own competence and judgment and that of his principal advisers in making decisions and carrying them out.

* By respecting the role of Congress, which shares major constitutional powers regarding treaties, war and peace, the armed forces, and the provision of resources.

* Congress in turn has an obligation to organize itself for the responsible exercise of its powers and for effective consultation and negotiation with the executive branch. Specifically, that implies leaders in the Congress who can represent it and speak for it.

Unfortunately these conditions have not been fulfilled in the Reagan administration. Though Congress is not blameless, the fault lies primarily with the President and the executive branch.

Objectives and means have not been suitably defined. Some have been too extreme, as in the rate of defense buildup or the approach to the East-West conflict. Others have been confused or unrealistic, as in Lebanon. Still others have been vague or misleading. In Nicaragua, for example, the explicit aim of the ''contras'' supported by the US is to overthrow the Sandinista regime, while Reagan has variously stated his objective as being to stop the arms flow to the guerrillas in El Salvador, to force a change to democratic rule, or to forestall another Cuba. In some cases, however, the original objectives have ''evolved'' toward a more moderate position.

The actual handling of foreign affairs has hardly been reassuring as to the competence of the administration. In his book ''Caveat,'' former Secretary of State Alexander M. Haig Jr. depicts a disorganized policy-process with many of the participants unqualified and working at cross-purposes, and with the President engaged only intermittently. Nor has Secretary of State George P. Shultz improved matters as many had hoped. The fiasco in Lebanon resulted from serious mistakes in conception and execution; the effort to shift the blame to the Congress reflects no credit on either Shultz or the President. And regarding Central America, according to some accounts, policy is being made by Caspar Weinberger, secretary of defense, and William Casey, director of the

Central Intelligence Agency, not Shultz.

The President has also not enhanced his credibility by calling Lebanon a vital interest (and then walking away), or by describing the stakes in Central America as a possible shift in the strategic balance. The administration, ignoring history and the Constitution, seems to view Congress as a mere intruder in foreign affairs.

Congress, it must be said, has not done all it could to facilitate cooperation. Until the late 1960s it was willing to entrust its leaders with authority to represent it in consulting with the president and his cabinet. Thus in the Eisenhower period, when Congress was Democratic, its leaders could negotiate to influence policy. In the 1970s, as the parties became weaker and individual members more independent, consultation became more difficult and less effective. Recently, however, there seemed to be a growing readiness to recognize a need for more leadership and discipline. But this is bound to be undercut when members are convinced that objectives are ill-defined, decisionmaking haphazard, and the prerogatives of Congress disregarded.

There appears little hope for more coherent bipartisan policy in this administration. The opportunity for reconstructing a moderate consensus has been frittered away. Given the disarray in the making and execution of policy, we should be grateful that our situation is no worse than it is - largely because we have not faced really grave crises which could be truly disastrous if bungled. But can we count on that indefinitely?