WHEN WE LAST looked in on them, the intellectuals of the French left were condemning our own culturally imperialistic television series "Dallas"--and Rebecca had just died in a plane crash, too, helas and alors. Such is the quality of mercy in France. To make things even worse, the French left has now taken a turn to the right. Is there nothing one can count on any more?

Max Gallo, the novelist and a spokesman for the Socialist government of President Francois Mitterrand, deploring this deplorable situation, has called on leftists to wake up and rally around with some invigorating ideas again, something to liven up a debate with. Enough of these Reaganiste ideas from across the Atlantic. At stake, he wrote with characteristic Gallic understatement, is not merely "the future success of the political left--but the very destiny of France." Not to mention the franc, now fetching a bleak eight to the dollar. After all, the argument goes, President Mitterrand himself is an admitted intellectual of the old (i.e., leftist) school. Surely, if only for old times' sake, he deserves a little more than the grudging acceptance by the defecting intellectuals of yet another free dinner at the Elys,ee Palace. The writers are as happy as ever to accept a meal there, Le Monde tells us, but they'd just as soon not advertise the restaurant.

And what sort of response did M. Gallo get to his heart-rending plea? Did the vieux gang rally to his cry? Did he hear from Simone de Beauvoir, from Michel Foucault? No, only from one Jean-Edern Hallier, the former editor of "Idiot International," a journal with which we are unfamiliar although we have ourselves been graced with the epithet from time to time. He challenged M. Gallo to a public debate. Or was it a duel? We forget. Whatever it was, M. Gallo ignored the challenge.

But that is not the main issue. The main issue is this: where was Mme. de Beauvoir? Where was M. Foucault? Perhaps they were watching television. "Dallas?" Never. Reruns of "Falcon Crest" would be our guess.