Boz Scaggs' new LP "Middle Man" (Columbia FC 36106) is a prize and a blessing to those disciples who have remained loyal to him through a few lean and even embarrassing records.

Scaggs' previous LPs were studies in style. From "Slow Dancer," a rudimentary blend of pop and club jazz, through "Down Two Then Left," a more energetic and solid mixture of jazz and rock, Scaggs evolved an eclectic routine in the hybrid of jazz, rock 'n' roll and club material. Cross-fertilization of these styles was particularly successful when the rock element infused the arrangements with a compacted, bridled energy. The integration of meoldic vocals with a percussive, instrumental drive gives punch to Scaggs' civility.

He has now matured in "Middle Man." Instead of a sense of experimentation in Scaggs' work, there is now a feeling of evolution and fruition. He has perfected the vocal and instrumental integration in "Low Down" and produced a style and sound reminiscent of the best of the big band front singers. Assisted by drummers Jeff Porcaro and Rick Marotta, Scaggs pushes the bank behind him -- much as Joe Williams, Frank Sinatra and Ella Fitzgerald drove Basie, Dorsey and Webb. That effort is best developed on the title track, the hit single "Breakdown Dead Ahead" and "You Got Some Imagination." Porcaro's drumming behind Scaggs' phrasing gives "Imagination" a slow burn, like heavy steam in a slow-motion roll.

Boz Scaggs pushes untiringly, driving the back-up, whether he sings a sultry, Parisian-flavored tango like "Simone" or an upbeat, funky tune like "Do Like You Do in New York." "Middle Man" is Scaggs comfortably nestled between the best of jazz vocalists and civilized rock 'n' roll.

Where Scaggs' "Middle Man" pays homage to a jazz tradition, Eric Carmen pays tribute to the roots of rock 'n' roll in his new LP "Tonight You're Mine" (Arista AL 9513). Carmen and producer Harry Maslin have assembled a studio band of seasoned heavy rockers like Billy Peak (guitarist for Chuck Berry), Kenny Passarelli (bassist for Elton John) and drummer Carmine Appice (from Vanilla Fudge and Beck).

Maslin produced the album after the flamboyant and percussive wall-of-sound style of Phil Spector, but without echo. "Lost in the Shuffle" uses guitarist Peak to resurrect the rock frenzy of Chuck Berry. "It Hurts Too Much" resembles a Ronette arrangement with Carmen's deep, volcanic voice set against a dense and monumental back-up. Other familiar voices surface from the album, including the Righteous Brothers, Rolling Stones and even Barbara Streisand in "Foolin Myself," a lush, almost melodramatic ballad.

Carmen is adept at reproducing the flavor and character of musicians who have, perhaps, inspired him. But "Tonight You're Mine" does not develop these influences to create a personalized or unique sound. The arrangements play like facsimiles. While Carmen's album is entertaining, its appeal is short-lived and constrained by nostalgia.