It was the most momentous of constitutional disputes, and it was no abstract lawyers' argument: The disposition of the war-powers controversy could determine whether hundreds of American military men faced the daily prospect of coming under fire.
The dispute posed two fundamental questions: whether the 60-day time limit in the War Powers Resolution constrained President Reagan's use of the Marines in Lebanon, and whether he had the constitutional power to keep them in hostilities without congressional consent.
The congressional interest lay in establishing that the time limit had been triggered and would require the Marines' withdrawal, and also in establishing that the President lacked sole constitutional authority to use the Marines in hostilities.
The President's interests directly opposed those of Congress. His representatives sought to establish that the War Powers Resolution posed no restraint on his warmaking power, and that it lay within his independent constitutional authority to keep the Marines fighting in Lebanon without congressional approval.
The compromise: no presidential acknowledgment that the 60-day time limit is binding, no presidential acknowledgment that statutory authority is constitutionally required - but congressional consent to keep the Marines in hostilities for 18 months, with no guarantee the President would respect even that longer time limit.
Congress drove a hard bargain. One wonders how its leaders emerged from the negotiations without agreeing to apologize for enacting the War Powers Resolution.
The 18-month compromise does nothing to establish the legitimacy of the resolution. It makes occasional reference to the resolution, but it takes no constitutional scholar to recognize those citations as verbal window-dressing. The compromise provides that ''the Congress determines'' that the 60-day time limit became operative Aug. 29. But the resolution obliges the President to make that determination, and there is nothing in the compromise to suggest that the President agrees with Congress as to when - or whether - the time limit was triggered.
More important than the statutory precedent is the constitutional one. The commander-in-chief clause confers upon the President only a narrow, emergency authority to use the armed forces in hostilities when there is no time to seek congressional approval. The War Powers Resolution expresses the sense of Congress that the President may use the armed forces in hostilities without congressional approval only in case of a ''national emergency created by attack upon the United States, its territories or possessions, or its Armed Forces.''
But the compromise contains nothing suggesting that, in its absence, the President would be without constitutional authority to use the Marines in hostilities in Lebanon. The administration never acknowledged that statutory authorization is constitutionally required. To the contrary, Secretary of State George Shultz testified that the compromise was not constitutionally necessary and, in fact, that the administration just might feel free to keep the Marines in Lebanon beyond the 18-month limit.
Had Congress the backbone, it could easily have protected its constitutional prerogative. It could have told President Reagan that he had a choice: either to file a ''hostilities'' report under the War Powers Resolution and recognize the constitutional necessity for statutory authorization, or to go it alone - and be prepared to take the heat himself when the casualties mount.
In the face of the administration's truculence, however, congressional approval carries all the logic of letting an arsonist torch your house so as to avoid the humiliation of having it done without your consent.
''We certainly want to avoid a constitutional confrontation,'' said the chairman of the House Foreign Affairs Committee, Clement J. Zablocki (D) of Wisconsin, ''and we have avoided that.'' Yes, Mr. Chairman, you certainly did.
Someday, perhaps, members of Congress will learn that confrontation-avoidance is not the consummate political good; that some constitutional principles are worth fighting for, even at the cost of momentary discord; and that procedural safeguards, once ignored to advance wise policies, are no longer present to block foolish ones.
Until then, the War Powers Resolution - and other laws aimed at curbing the abuse of presidential discretion - will remain rickety fences awaiting a stampede.