Guess what the Sensitive Young Man is doing for "The First Time" in the French film by that name. Guess with whom he does it first, and how much it costs him from his allowance. Guess with whom he does it second, and how much it costs him of his heart.

Actually, there is no need to guess, as long as we are in this period of passionate nostalgia for our own individual pasts, which, in the case of people who were teen-aged in the Fifties, fits in so nicely with the general nostalgia for the period. Anybody who can muster up a bittersweet memory of sexual longing is in business as a culture hero.

The only wonder of it is that these experiences are all identical. There is always the book hidden under the bedclothes, the inability to picture parents doing it, the brush with homosexuality, the ceremonial visit to the prostitute, the locker-room talk afterward, the disillusionment, the search for the nice girl who will also come across, and so on. Claude Berri's film goes right through every part of this familiar confession, using a quartet of look-alike homely French teenagers in a background of the Parisian lower rent district, always with sunlight and closeups of eyes to stress the point that each young man is very sensitive.

But is he? Why are these reminiscences always populated with girls who are not only fresh and romantic but free - anxious to run off after the blissful experience, leaving the young man with the luxury of being melancholy, instead of having any responsibility for the girl. As much as one can understand the urge to leave these tedious young men, this ignores what this era meant to Sensitive Young Women. Just as the S.Y.M.s had a need, quite besides the sexual urge, to see how many women they could get to "do it," the S.Y.W. had a need, besides the sexual one, to see how many boys they could annex romantically. What these reminiscences are skipping, by having the girls run away, is probably a post-sexual scene in which the boy explains that he can't become seriously involved with her because she is, by definition, proven to be "not nice."

And in fact at the end of "The First Time," the soulful look in the boy's eyes and the sunlight sparkling on his frolicking family leave no doubt that he now knows he will never follow The Girl but wait, so that some day there will be, for him, a Nice Girl, Like Mother.

It is a story that will not seem unbearably trite and smug only if the reason the Sensitive Young Man is telling it to you is that you are that Nice Girl - or, possibly, his mother.