There once was a movieland New York City that was a colorful playground for lovers. Kaleidoscope courtships whirled from carriage and boat rides in Central Park to a glittering Fifth Avenue, to standard tourist spots made fresh with laughter and kisses.

But we see that city, and certainly romance, as a lot grayer now, and Woody Allen's "Manhattan" is the wittily updated version of modern love in New York, shot in black-and-white film that is actually tones of gray.

Only the landmarks and the Gershwin tunes are the same. These lovers don't have any problem finding each other; the problem is that they are trying to find themselves. You don't fall in love with someone for what he or she is any longe, but for how that person fits your needs of the moment. Hearts are never broken by deceit - honesty serves the purpose just as well. A sufficient exit line is, "So I made a mistake. What do you want me to say?" and a compassionate one is, "I wish you'd get angry."

Allen now has this world down with exquisite subtlety. When he tried to be profound about eternal human nature in "Interiors," he failed, but this film succeeds because it uses his fine talent for showing external human behavior under current cultural influences.

Allen's previous comic persona, as life's loser, has grown. It is no longer predictably preoccupied with fussing over childhood rejections, meeting girls or anticipating defeat and, by extension, death. A warm and quick-witted homely little guy does quite well in the superficially sophisticated society shown here, where the impossible rules of the game make everyone a loser by definition. Michael Murphy, in a funny extension of his "Unmarried Woman" role of loving both wife and mistress, seems to fare worse.

It is a tiny society, educated, successful and cripplingly insulated and introspective, bounded on four sides by Elaine's fashionable eatery. When the hero confides - to the perfect modern confidante, a tape recorder - what makes life worth living, his list starts with Groucho Marx and builds up to Swedish movies.

Life's difficulty for him is not finding women to love him, with all his quirks, but in the destruction to which this peculiar love inevitably leads. His first wife was "a kindergarten teacher who got into drugs, moved to San Francisco, became a Moonie and is now with the William Morris Agency." His second wife, played by Meryl Streep using her renowned luminosity ironically, left him "for another woman," and is peddling the story of their marriage to the movies. But because his girlfriend, to whom Mariel Hemingway brings gave charm, is a simple high-school girl who plain loves him, he feels obliged to supply the difficulties that lead to modern love's climax, which consists of a hurt person crying while the inflicter of hurt also plays magnanimous role of comforter.

One of the best comic scenes occurs after Diane Keaton, deftly infuriating as the Allen character's new love, runs into the incredibly sexy and brilliant ex-husband she kept describing. Beautifully sketched in by Wallace Shawn, he is a sweaty, anxious small man, bald and fat, and Allen is profoundly shocked. You feel that he alone sees beyond the conventions of this group, which declare that a clever man's looks don't count at all, to a real world out there, where the minimum standard for a "ladies' man" is that he should be taller than the lady.

It is this fleeting glimpse of out there, beyond these people's Manhattan, that gives "Manhattan" its meaning, as well as its humor. At a chic ERA party, Allen mentions that Nazis are marching in New Jersey, and is assured that they have been taken care of by a satirical co-ed piece in The New York Times. "I think really biting satire is better than physical force," someone concludes, to which Allen reples that no, he thinks physical force is probably more effective with Nazis.

But biting satire is most effective with Woody Allen's "Manhattan." CAPTION: Picture, WOODY ALLEN AND DIANE KEATON ON A "ROMANTIC" BOATRIDE IN "MANHATTAN."