What happens when a single Supreme Court decision strikes down in one fell swoop, as Justice White put it, provisions in more laws enacted by Congress than the total of those invalidated in the past?
For one thing, after last week's ruling against these ''legislative veto'' provisions, there were some immediate predictions which ought to be invalidated too. They threaten governmental conflict and even chaos in reaction to a change that should lead to cooperation and rationality instead.
Rationality can be served in at least two ways. By the already promised congressional hearings to explore just how present laws and pending legislation may be affected. By the Supreme Court's spelling out its meaning in cases beyond the 1975 deportation incident that brought its sweeping June 23 decision.
Uncertainties have arisen because the legislative veto takes various forms in various laws. Essentially it permits one or both houses of Congress to reverse or restrain powers delegated by Congress to the president or executive agencies. It can be used to overturn a regulation of the Federal Trade Commission, for example, or to put strings on arms sales, to pull back troops committed by the president in an undeclared war.
Sometimes presidents have found the legislative veto an acceptable price to pay for gaining broad powers. More often they have complained about it. Liberals have favored it in some circumstances, conservatives in others. Its many-sidedness may be suggested by President Reagan's opposition to it now, even though he favored it before he was in office as a way to make regulators more sensitive to the mood of the people. Dissenting Justice White is concerned that the ruling against the legislative veto may make it more difficult to ensure that ''the fundamental policy decisions in our society will be made not by an appointed official but by the body immediately responsible to the people.''
Such considerations did not deter the court from finding, by a 7-2 vote, that the legislative veto violates constitutional separation of powers. In effect, it came down on the side that Congress has the power to pass laws affirmed by both houses and signed by the president - or passed by two-thirds vote over presidential veto. Congress does not have the power to maintain control of those laws through later decisions that do not have to go through such a process.
This approach has the merit of requiring positive action for intended results. It is a little like asking Congress to pass spending subsidies for each intended purpose as opposed to letting tax breaks provide endless silent subsidies through ''tax expenditures.''
The predictions of conflict now look toward possible congressional efforts to compensate for the legislative veto with laws delegating only very narrow powers - and possible administration efforts to take advantage of freedom from legislative veto to abuse regulatory or military prerogatives.
Which brings us back to the need for cooperation rather conflict mentioned at the outset. As the dimensions of change are explored, good faith on all sides could result in cooperative rather than adversarial means to foster constructive workings of the law.
Congress still can rein in government agencies with its control of the purse strings. It can use such means as ''sunset'' legislation - setting up an agency for a limited time, subject to renewal on evidence of good performance. Even nonbinding resolutions could serve to make ''the mood of the people'' felt.
After all, it is the people to whom all three branches of government must ultimately be responsive - as the court has now freshly challenged the other two branches to be.