The Founding Fathers, whom we have been celebrating, left plenty of room to grow in the Constitution. Future generations, they obviously thought, should be free to adapt and modify the infinite uses of democratic government.

But given their feelings about royalty in general and George III in particular, it seems allowable, or even indicated, to imagine them turning over in their graves about the recent Supreme Court decision on presidential immunity.

Many Americans, it is true, would have deplored the court's finding at any time. But having it come right after the 10th anniversary of the first act in the all-time abuse of presidential power makes it especially grating.

One of the great and continuing challenges of our system is to exalt presidents so they can behave better than the rest of us while at the same time making them understand that they really are merely first among equals.

The first thing that happens to a president is the realization that he is different. That is partly due to the way he lives--never taking a suit to the cleaner, never having to argue with a plumber. We arrange that for him so his mind is left free for the cosmic.

The trouble is that they get the idea that it is all theirs.

"They are all my helicopters, son," Lyndon Johnson memorably told a young soldier.

In his manner, Ronald Reagan has resisted the imperial strain, but he is showing those tell-tale, possessive signs lately. He refuses to explain to us why Alexander M. Haig Jr. stalked off the job as secretary of state. The public has no need to know, Reagan says. It is his Cabinet, he thinks.

Supreme Court Justice Lewis F. Powell Jr. gave a curious, unreassuring explanation of the majority verdict on immunity: the press is constantly scrutinizing presidents. Well, yes, the press will, if it gets the chance. But this administration has been trying to curtail the Freedom of Information Act that in many instances is, if not the only, surely the best, hope of finding out what the chief executive is up to.

Powell wrote also that "vigilant oversight" by Congress is a deterrent to abuses of office. It is Congress' duty to "make credible the threat of impeachment," he noted.

But impeachment is a nuclear remedy, undertaken with the utmost reluctance by Congress and the country. It took months of agony for the House Judiciary Committee to gear up for action against a president who acted in distressing, preemptive accord with the words of the decision, regarding immunity as "a functionally mandated incident of the president's unique office, rooted in the constitutional tradition of the separation of powers . . . . "

What makes the decision even more puzzling is that the case involved that president, Richard Nixon. It was brought by an exemplary public servant, and citizen, A. Ernest Fitgerald, who has been engaged in a 12-year fight against executive arrogance.

Fitzgerald, a Pentagon cost analyst, was fired in 1970 for doing his job. He reported the $2 billion overruns in construction of the C5A transport plane. In his $3.5 million suit, based on evidence found in the Watergate tapes--"Get rid of that s.o.b."--Fitzgerald charged that Nixon had conspired to render him a permanent unemployment statistic.

But, the high court majority ruled, a president has absolute immunity against lawsuits.

"A reversion to the old notion that the king can do no wrong," wrote Justice Byron D. White in a vehement dissent.

"I find it ironic, as well as tragic," he wrote, "that the court would so casually discard its own role of assuring 'the right of every individual to claim the protection of the laws . . . in the name of protecting the principle of separation of powers.' "

What some find equally ironic is that in another controversial case of immunity, White came out on the opposite side.

He wrote the majority decision in Stump v. Sparkman, which held absolute immunity for the judiciary. A judge named Harold D. Stump had ordered, on the mother's say-so, sterilization of a 15-year-old girl without her knowledge or consent. Judge Potter Stewart, dissenting, found in Stump's conduct "a total absence of any of the normal attributes of a judicial proceeding."

While acknowledging that pain had been inflicted on an individual citizen, White ruled on the superseding importance of the principle of judicial immunity.

We have no way of knowing what moved White to argue in the Nixon case that no man should be above the law. Possibly, he makes a distinction between judicial and executive immunity. Justices are not required to explain what appear to be inconsistencies in their decisions. They are shielded from inquiry. But you can't help wondering. The Founders were much in favor of wondering citizens. They seemed to feel they would preserve the Republic.