Life's a crapshoot, so why should picking the duet partners for Rhythm, Country & Blues have been any different? ''No one knew how these voices would merge,'' says producer Don Was, ''so all we could do was try to combine interesting personalities-like Al Green's flamboyance coupled with Lyle Lovett's more internalized energy. You just figured something of interest was going to happen.'' As predicted, Lovett proved the perfect foil to Green on ''Ain't It Funny How Time Slips Away.'' ''Lyle made a really wise decision to not try to outlick Al, which I don't think anyone on earth could do,'' says Was. ''Instead, he stayed true to his character and kept the energy very contained. They never crossed turfs.'' It also helped that, unlike with Frank Sinatra's Duets, the 11 pairs on Rhythm recorded in the same studio at the same time. That, and using first or second takes on most of the cuts, gives the entire proceedings a tangible immediacy-or, in the case of Travis Tritt, cause for extreme panic. ''I knew Patti LaBelle could cut me up into small pieces if she wanted to,'' says Tritt, who sings with her on ''When Something Is Wrong With My Baby.'' ''But every time she did something that amazed me, it pushed me to try to equal that-although I had no chance of even getting in the ballpark.'' For Little Richard and Tanya Tucker, the challenge was more, well, balanced. ''They were both firecrackers,'' says Was. ''All I had to do was capture the energy.'' Their track-''Somethin' Else''-also gave Was a chance to make the kind of rockin' Little Richard cut he wanted to hear. ''Little ! Richard's early recordings for Specialty (Records) are like the greatest rock & roll ever,'' says the producer. ''I was trying to reproduce that same sound.'' So was Little Richard. Belting out Eddie Cochran's classic reminded him of his long-ago hit ''Keep A Knockin'.'' ''Oh,'' he shrieks as only Little Richard can. ''I got a chance to scream one more time. One more time. Whooo!''