Federal District Judge Gerhard Gesell made the right decision Friday at a key point in the Oliver North case.

If his decision had gone the other way, it could easily have dwarfed even the verdict on North's guilt or innocence in terms of its impact on how America is governed.The decision: Not to call former President Reagan to the witness stand in the criminal trial of North on charges of hindering a federal investigation into the diversion of funds from Iranian arms sales to the Contra rebels in Nicaragua.

If Ronald Reagan had been hailed into court, he would have been the first president or ex-president ever forced to appear in a courtroom. The key word is "forced." Other chief executives have testified in various cases - but only at their own volition.

Though Judge Gesell claimed to have what he calls the "naked power" to compel Reagan to testify, he was well-advised not to try to exercise it. Such an attempt could have constituted a major breach in the constitutional separation of powers between the executive and judicial branches of government and might itself have resulted in a legal battle that could have tied up the courts for years.

Besides, there are other ways of getting information sought by the defense - which insists that North was acting under White House orders in the Iran-Contra scandal - without setting a dangerous precedent or imperiling North's right to a fair trial.

One way would have been to take a deposition from Reagan. Another would have been to let Reagan answer lawyers' questions on videotape, as previous ex-presidents have done in other cases. Such procedures are desirable because they could guard against hasty, careless answers that could embarrass some of America's allies or let out secrets whose exposure could erode national security.

The overriding principle, though, is that this nation's chief executives need to be protected from lawyers seeking to create headlines, harass them for unpopular decisions or maybe just divert attention by creating a red herring.

The efforts to put Reagan on the witness stand in the North case seem to fall into the last category. Even if it could be proved that North was somehow following orders, that still would not relieve the former colonel of his own legal responsibility. As the Baltimore Sun notes, "Subordinates, even in the military, are specifically required to place the law over orders."

By quashing an effort to drag Reagan into court, Judge Gesell has avoided creating a legal precedent that could have done lasting damage.