Two years and two months after the Iran-Contra scandal broke, and with the cost in lawyers' time and expenses already running at $16 million or more, the criminal case against former White House aide Oliver L. North is finally going to trial.

A chance for a pardon before trial gone, home now from the lecture circuit and the task of raising upward of $3 million in legal defense fees, the retired Marine lieutenant colonel settles down Tuesday morning in a federal courtroom here for a stay of perhaps five months or longer.A stubbornly determined federal judge, 78-year-old Gerhard A. Gesell, has pushed the case over the last of its pre-trial barriers, through a maze of paper, past a gantlet of intelligence agencies, and beyond the repeated trips of lawyers up to higher courts and back. The judge said privately last week that nothing stands in the way of a Tuesday beginning - four months later than the judge had wanted it to start.

The North trial - the first, and possibly the only one, to result from the scandal - will be narrower in scope than it once promised to be. Still, it is likely to be a showy event that could even bring former President Reagan to the witness stand.

It may reveal little if anything new about the scandal, yet it is likely to be one of Washington's most closely followed events.

It could be a test of whether, in the estimate of the nation's people and its politicians, North remains something of a folk hero: a darling of television, the object of a brief but adoring fad of "Ollie-mania," a "national hero" (at least in Reagan's words).

This time, though, North's future and his fate rest in the hands of 12 jurors, to be chosen out of some 300 citizens summoned for potential duty.

And the trial will not be a public spectacle to match the televised congressional hearings in 1987. No cameras are allowed in federal courthouses; North thus will be seen on TV only in artists' sketches, in news film of his arrivals and departures outside the U.S. Courthouse at the foot of Capitol Hill, or in repeats of telecast scenes before Congress.

The former Marine and National Security Council aide won't be wearing his Marine uniform or his ribbons; now retired, he is expected to wear a dark business suit. And he may never take the stand; only his lawyers have an idea about that, at this point.