THE ALBUM -- Ry Cooder's "Borderline," Warner BSL 3489.

If it's fine details about the trailblazing of America you seek, 14th and Constitution is as good a place to begin as any. But if you're curious about the pioneering of popular music, there's hardly a more erudite authority on the subject than Ry Cooder.

Cooder has long been a one-man compendium of American musical history, as evidenced on albums like "Chicken Skin Music" and "Paradise and Lunch." But like any good historian, Professor Cooder knows that preservation entails more than brushing the dust off an artifact, tagging it and putting it under glass. And nowhere has his special talent for merging past, present and future been so delightfully displayed as on his most recent album, "Borderline."

The cover is of a piece with most of the songs it contains: A female matador strikes a pose of balletic confidence as the wild-eyed bull, on whom the picadors have already performed their sanguinary task, makes the fatal hubristic rush. A little dramatic, perhaps, but a nice balance for the literal sparseness inherent in tunes lamenting the way we wound ourselves with love, only to charge at it again before the blood dries.

For the opening track, Cooder has unearthed "634-5789," and though its jaunty tempo and soul-flavored swagger evoke Sam and Dave, Cooder has typically eschewed the shyly gospel, girlish style of the original -- along with Ma Bell's obsolete prefix. (Remember, on "Beechwood 4-5789," the Marvelettes' tentative offer, "You can call me up and have a date any old time"? "call me on the telephone!" dares Cooder, and leaves it at that.)

It's this spread-legged stance of sexual and social bravado that Cooder maintains on the nine songs that follow, but the X-ray vision provided by his interpretations -- and by the ironies that make them as much a part of rock today as ever -- reveals his toes to be wriggling insecurely beneath the boot leather.

The protagonist of "Speedo" brags about how unsafe everyone else's girl is in his presence, but in "Why Don't You Try Me," our bathetic hero waits until he's overheard a lover's quarrel before stepping into the hall to pose the title question. And the narrator of "Down in the Boondocks" is the very voice of defeat, an effect accomplished in part by Cooder's insistence on putting the melody layer below the harmonies, instead of on top as in the Billy Joe Royal version.

But Cooder crosses many peripheries other than the traditional sexual ones.

There are a commingling of black roots with white, a crossing-over of rhythm and blues with country/western and a veritable merger of Tex-Mex and Brill Building pop. The ghosts of Huey P. "Crazy Cajun" Meaux and the Sir Douglas Quintet hover over "Crazy 'Bout an Automobile," and on "Try Me" and the Jennings/Hooper tune, "Never Make Your Move Too Soon" one finds oneself visiting Motown and Memphis on the same bug-spattered bus.

Cooder crosses all these borders with ease, mainly because his love of American musical forms and his commitment to keeping them honest grants him a carte-blache visa. His concession to pop's future is a stubborn penchant for using the 3M digital system, a wonderful innovation that is nevertheless apt to be irritating to those without the hardware to appreciate it fully.

But considering what marvelous lessons Cooder imparts, who's going to complain if he occasionally jumps ahead a chapter or two?