The discovery of original manuscripts by George Gershwin, Cole Porter, Richard Rodgers, Vincent Youmans, and others in a Warner Brothers warehouse in Secaucus, N. J., has been greeted with the excitement usually reserved for events like Schliemann's unearthing of Troy. And why not? Yesterday's popular songs constitute a kind of archaeology of the heart - in this case, up to 70 crates worth of ''triumphal find,'' in the words of Miles Kreuger, president of the Institute of the American Musical.
A recent New Yorker cartoon depicted one turtle saying to another as a third turtle ever so slowly approaches: ''Oh dear. Here comes Mr. Nostalgia.'' And certainly any dig that brings to the surface the complete Broadway scores of Gershwin's ''Pardon My English'' and Porter's ''Gay Divorce'' (later made into the 1934 movie ''Gay Divorcee,'' starring Ginger Rogers and Fred Astaire) is bound to lead to a few strolls down Memory Lane, as popular songs used to put it.
But, in the spirit of the archaeologist, one can also go a little further than nostalgia and venture a few high-flying theories about civilization, way back then. Let us narrow the company to Gershwin and Porter and take as our thesis: American popular music in hard times.
Alec Wilder, a distinguished composer himself, has observed of Gershwin: ''The years of his greatest popularity were those of the Depression.'' Wilder argues that Gershwin understood then what the country needed, and that the ''insistently cheery sound of his music'' was less his instinct than his shrewd response. Gershwin's up-tempo tunes buck you up. The very titles chuck you under the chin and slap you on the back: ''Strike up the Band,'' ''Clap Yo' Hands,'' '' 'S Wonderful.''
Gershwin, the boy from Brooklyn, seems to send up signals of hope from the heartland, while Porter, the boy from Peru, Indiana, made smart faces at the Depression, dressed in top hat and tails, peering down, as it were, from a penthouse at the Ritz. It has been remarked of Porter that the closest he ever got to the farm, once he left, was to write a tune called ''An Old-Fashioned Garden.'' He passed for the Scott Fitzgerald of popular music - keeping the saxophones wailing and the gold slippers shuffling, regardless of what was happening in the streets.
Gershwin composed bracing motifs - more rhapsody than blue. Porter snapped his manicured fingers and drove the party on. From New York to Paris, the word was ''C'est magnifique'' - with only a twist of irony at the corner of the mouth.
A popular composer - until rock came along - was always judged by one question: How did he or she sing of love, as in moon-and-June? Even here the economy did not appear irrelevant for the composers of the '20s and '30s. Porter wrote songs of glittering invulnerability, like ''Just One of Those Things,'' that treated all ups-and-downs - financial or romantic - as tests one should tough out, elegantly.
Gershwin, on the other hand, cuddled up against the cold in the lyrical enclaves provided by songs like ''Someone to Watch Over Me.''
If, in the face of the history of the '30s, Gershwin seems a little naive, and Porter more than a little oblivious, their music worked the modest, temporary enchantment that is the duty and justification of all popular entertainment.
Will there be a new manuscript or two in the Secaucus warehouse, never heard before? The crate-openers hint as much, and we can hope so.
Gershwin may sound like a band at half-time, playing victory marches when the score is 38-0 against. Porter may appear as heartlessly blithe as a man tap-dancing past a bread line on his way to his Rolls Royce. But the jazzy, sentimental voices of American popular music - tirelessly zippy and youthful, forever bouncing back - are not to be despised.
In giving the public what it wanted to hear, these two composers (and others) gave a little more than just that. The stylized Porter impudence can border on genuine courage. If Gershwin wore his Valentine heart on his sleeve, it was, on occasion, a real heart. In hard times half a century later, we who knew these songs as children can use the echoes now.
Keep opening those crates!