With a bit of judicious juggling, RONNIE MILSAP'S "Keyed Up" could have been a swell concept album, along the lines of Willie Nelson's "Phases and Stages." Of the 10 songs, eight deal directly with marital blues, but they're presented without any sense of order that might have implied either dissolution or reconciliation. Milsap, a compelling and virile singer with one foot planted in country and the other in pop, kicks things off with "Stranger in the House," a bitterly paranoid "is she or isn't she?" cheating song. It's followed by a bit of MOR advice to the lovelorn, "Show Her"; a more typical country complaint, "Don't Your Mem'ry Ever Sleep at Night"; and a caustic warning, "Watch Out for the Other Guy." On the second side, Milsap sighs "Don't You Know How Much I Love You"; admits resignedly that "Feelings Change" (with the optimistic coda that what's bad can perhaps be good again); and finally, with the prospect of getting back together with his wife, wonders "Is It Over?" (her affair, not the marriage). There's also "Like Children I Have Known," with parallels drawn between feuding kids ("It's not a dollhouse,/ It's a home) and a couple fighting over possessions. Again, there's an optimistic fillip, with Milsap opting for the children's "kiss and make up" solution. The story of a troubled marriage is all there, and home tapers would do well to reorder the material. The other two songs are throw-ons, the silly "I'm Just a Redneck at Heart" and the Pollyanna-ish "We're Here to Love." Throughout, Milsap's in fine voice, his keyboard work fluid and brittle enough to punch the songs above the ubiquitous Nashville String Machine. The BELLAMY BROTHERS are the most successful duo in country music today. Their familial harmonies and amiable brand of easy-listening country have lightened the airwaves considerably. Rooted in the brothers' acoustic guitars and simple arangements for melodically catchy tunes, the music suggests a blend of the Eagles, Marshall Tucker Band and fellow-Floridian Jimmy Buffett. Although the area of interest is standard country -- its basic parameters being the bedroom and the barroom -- the Bellamys keep things warm, genial and devoid of beer-stained angst. Their latest album, "Strong Weakness," has its share of future hits, including several languid, soft-spun love ballads in the Don Williams vein, "Doin' It the Hard Way" and "Long Distance Love Affair" ("Your voice is here,/ Your body's there"). "I Love Her Mind" might fit the Williams mold, except it finds the boys getting a little playful with women's lib (they love "her mind" because it comes up with new ways to make love). Throughout, the harmonies are delightfully natural, the band support tight and tasteful. The brothers are also in the stores with a "Greatest Hit" package, a zesty romp through the last six years of their music. Among the offerings: the gently pointed "If I Said You Had a Beautiful Body, Would You Hold It Against Me" (and its inevitable followup, "Do You Love as Good as You Look?"); the Jamaica-flavored "Get Into Reggae, Cowboy" and "Redneck Girl"; and the achingly elegiac "You Ain't Just Whistlin' Dixie." It's all bright country pop, pleasant as a Florida breeze and tangy as a Florida orange. RONNIE MILSAP -- "Keyed Up" (RCA AHL1-4670- A) THE BELLAMY BROTHERS -- "Greatest Hits" (Warner Bros./Curb 23697-1) and "Strong Weakness" (Elektra 9 60210-1). Milsap, the Bellamy Brothers, Joe Stampley, Louise Mandrell and the Kendalls perform at the Bull Run Country Jamboree, Saturday from noon to 7 at Bull Run Regional Park in Manassas.