''Mel Torme and Friends/Live at Marty's, New York City.'' Mel Torme, vocals and piano; Mike Renzie, piano; Jay Lenhart and Eddie Gomez, bass. Finesse W2X 37484. - Torme has it all - the voice, the technique, the feel for jazz, the professionalism, the sense of humor, and the way with a lyric. In this live two-record set he is joined by friends Janis Ian, Cy Coleman, Jonathan Schwartz, and, most notably, Gerry Mulligan, in a romp through numerous show tunes, jazz numbers, and medleys. It's a slick and entertaining performance, which Mel tosses off with savoir-faire, and it's full of bright musical moments - thoughtful versions of some lovely ballads. Torme accompanies himself on the piano for a ''Porgy and Bess'' medley, but friend Gerry Mulligan contributes to the best moments on the album. ''The Real Thing,'' a Mulligan-Torme collaboration, has got to be one of the - if not the - most beautiful tune in recent memory - Torme sings his socks off on it, and Mulligan follows with a poignant solo on baritone sax. Then the two jump into a great Mulligan medley, with Torme using his voice as the second horn on ''Line for Lyons,'' ''Venus de Milo,'' and ''Walking Shoes.'' But it wouldn't be fair to write about this album without mentioning Torme's pianist, Mike Renzie. An outstanding soloist as well as an astonishingly sensitive accompanist, Renzie is one of a rare breed that can fulfill both those roles with equal aplomb.