Both Kenny Rogers and Crystal Gayle, who open a two-night stand at the Capital Centre tonight, have succumbed to their own successful countrypolitan formulas.

While both have country roots (Rogers less so than Gayle, who will never be allowed to forget she is Loretta Lynn's younger sister), they eventually discovered that pop went the audience. They homogenized their music to the nth degree. After Rogers' "Lucille" and Gayle's "Don't It Make Your Brown Eyes Blue," their music lost its surprise.

"We've Got Tonight" (Liberty LO-51143) is Rogers' last album for that label; he recently signed a deal with RCA for a reported $20 million. Rogers, a genuinely charismatic pop phenomenon, has often qualified himself as a "commercial" rather than a "good" singer, adding that he has a knack for picking hit material. Make that 'had' because the knack is hardly evident on this oddly unemotional and low-key album. There are no "Gambler"-style morality tales this time around, with the possible exception of the lilting Harry Chapin-like "Scarlet Fever."

Most of the songs either fail to impress or suffer in comparison with original versions. Bob Seger's tender title ballad is given an unexceptional duet reading with Sheena Easton, while Billy Preston's enchantingly simple "You Are So Beautiful," already covered by a half dozen artists, is dreadfully straight-ahead. Rogers doesn't invest either song with the warmth he so often displays in concert and, as a result, they fail to engage on any level.

Elsewhere he mines familiar lodes: "Love, Love, Love" expands on the "don't give up on love" and "you picked a fine time to leave me" themes that in one form or another have dominated his music since "Lucille." "No Dreams" has a "Lady"-like edge of confession with a denouement that's sure to please the fans: "Guess I'll just go somewhere far away and hide away and heal." It sounds like a Lionel Richie song (it's not), and it is vastly better than the actual Richie contribution, "How Long."

Richie has written some memorable love ballads, but "How Long" is an embarrassment that refuses to overcome a promising melody. The only way Rogers could get away with lines like, "How long till I touch, till I hold you, till I see you again" and "I've been waiting for a girl like you/One that I can call my own/Tell me if this dream of mine will come true/Girl I'd really like to know," is to sing them in Italian and pass them off as opera. Light opera. Or soap opera--except that it doesn't wash.

The album is further weakened by a lack of direction in the production end. Rogers produced some of the cuts and various teams did others. "Bad Enough" sounds like the singer listened to Val Garay's "dirty pop" approach but couldn't match its assurance. The only instrument that jumps out anywhere is Steve Luthaker's all-too-brief guitar solo on "All of My Life." Otherwise the sound is polite and bland, too often surrendering to syrupy string arrangements. As a result, not one of the songs has the kick--emotional or sonic--of Rogers' last significant single, "Love Will Turn You Around."

In recent months, Rogers has trimmed his weight by 40 pounds. He would do well to follow a similar path in his music, cutting away the pop veneer and redirecting his energies to finely crafted songs and more emotionally engaging performances. Like his friend Richie, Rogers has proved in the past that he's capable of much better work than this.

Crystal Gayle never did seem comfortable with straight-ahead country; her style of pop-country is easygoing and uncluttered. That's not surprising since her longtime producer is Allen Reynolds, who molded Don Williams' mellow country sound. Since moving to Elektra, Gayle has expanded her team to include ace Nashville producer Jimmy Bowen. Her clear, generally unaffected soprano is well suited to their production aims, but like Rogers, she suffers from weak material.

"True Love" (Elektra 9-60200-1) is pleasant without being memorable, with a commendable diversity of styles. "Our Love Is on the Fault Line" has a perky California bounce. One imagines both the Eagles and Nicolette Larson being comfortable with it. "Everything I Own," a Bread staple from the '70s, is pretty but threatens to sink into Rita Coolidge soporifics. "Till I Gain Control Again," the classic Rodney Crowell anthem, is a bit flat and suffers from comparison with other versions. It would be better if Gayle took her own advice from Roger Cook's rhythm and blues offering, "Let Your Feelings Show."

It's something she does, oddly enough, not on her own album, but on the soundtrack to Francis Coppola's "One From the Heart" (Columbia FC37703). Tom Waits' score may be making a belated appearance, but the music has a far stronger impact on vinyl than it did in the film. Waits is a student of affected jazziness, a graduate of the cool school. Teaming a gravel- voiced hipster with a conventional pop singer may have seemed a bad idea, but it turns out to be an inspired match. They bring out the best in each other, Gayle tempering Waits' unfocused exuberance, he inspiring her felinity and emotion.

Waits and Gayle serve as musical surrogates for Coppola's celluloid couple, charting the ups and downs of an affair. Working within the constraints of Coppola's fervent imagination rather than his own, Waits has come up with some of the best songs of his career. And Gayle responds with the kind of looseness and inner energy that is absent from "True Love."

Both artists went outside their traditional parameters for "One From the Heart," and discovered--or at least displayed--unsuspected talents. There's a lesson there.