Jazz is officially "a rare and valuable national treasure" -- last week the Senate passed a bill proclaiming it so.

So tell us something we didn't know.

But if anyone is in need of further convincing, they should sit down with two newly compiled treasure troves of past glories: "Singers and Soloists of the Big Band Era" (Smithsonian Collection of Recordings 19881) and "The Erteguns' New York: New York Cabaret" (Atlantic 81817). Taken together, these generously programmed, six-record volumes provide an overview of an era, and indirectly trace the evolution of the singer from just another soloist to center-stage star.

"Singers and Soloists" can be considered a companion to the Smithsonian's spectacular "Collection of Classic Jazz" and "Big Band Jazz: From the Beginnings to the Fifties",which were dedicated to the great ensembles. Jazz critic Martin Williams again selected the tunes -- 94 of them, focusing on the swing era, beginning in 1929 and choosing 1959 as the cutoff date. Wherever you drop the needle, you'll find a gem.

The spotlight is on the singers and instrumental soloists associated with the great orchestras, most of whom built their names with radio and personal appearances at dance halls. In big-band days, jazz and blues merged with the popular song, providing one of the few arenas where black and white performers and composers could mingle without comment. At the start of the swing era, the band vocalist, often a pretty "girl singer," was treated as just another instrument in the ensemble. Homogeneity was the ticket -- distinctive voices and personalities were subjugated to the will of the bandleader. But as the record shows, the solo singer eventually emerged triumphant.

The dance program begins with Bing Crosby "After You've Gone" a 1929 performance with Paul Whiteman and His Orchestra. Crosby, then still a member of the Rhythm Boys, only takes one chorus, but his verve and purity of tone are unmistakable.

Louis Armstrong set the standard for soloists, expressing elasticity and inventiveness as an instrumentalist and a commanding persona as a singer. The six Satchmo selections here include "(What Did I Do To Be So) Black and Blue," one of the first racial protest songs and one of Armstrong's signature pieces, Lil Hardin Armstrong's "Struttin' With Some Barbecue."

The bandleaders often stepped to the mike themselves: Cab Calloway distinctively fronts his Cotton Club Orchestra, singing "Zaz Zuh Zaz" and "My Gal"; Bunny Berigan takes a charming vocal solo and follows it with a trumpet cadenza on "I Can't Get Started"; and Jack Teagarden puts down his trombone for a resigned reading of "I Gotta Right to Sing the Blues."

More often, though, the singers became identified with certain orchestras. Jimmy Dorsey had Helen O'Connell and Bob Eberly; Tommy Dorsey had Frank Sinatra and Jo Stafford; Benny Goodman worked with a series of stellar singers such as Mildred Bailey, Helen Forrest, Charlie Christian and Peggy Lee.

These bands were a proving ground for singers, a way to prove you were not just another pretty voice. As Lee says, "I learned more about music from the men I worked with in bands than I've learned anywhere else." Here we hear two sides of Lee, a creamy-voiced "girl singer" on "How Deep Is the Ocean" and dusky vamp on "Why Don't You Do Right?," which shows where she's headed.

By the '40s, the singers were beginning to assert themselves in the arrangements. A boyish, light-voiced Frank Sinatra is almost unrecognizable on "Daybreak," but the seeds of his phrasing are beginning to develop. Lena Horne glows darkly in "You're My Thrill" with Charlie Barnet and His Orchestra. Other luminaries include a spry Ella Fitzgerald bubbling through "Undecided" and "Have Mercy" with Chick Webb and His Orchestra; and Sarah Vaughan gliding through "I'll Wait and Pray" and "Lover Man" during her short stays as a band vocalist with Billy Eckstine and Dizzy Gillespie. The collection also touches on many other essential singers: Ivie Anderson, Anita O'Day, Doris Day, Kay Starr, Pearl Bailey, June Christy, Chris Connor, Joe Williams . . . And the songs: "Body and Soul," "In a Sentimental Mood," "Happiness Is Just a Thing Called Joe."

Most of the selections have been previously released, but it's a pleasure to have them gathered in one place. Rarities include a sampling of Billie Holiday's brief but important tenure with the Count Basie Orchestra. The recordings of "I Can't Get Started," "Swing! Brother, Swing!" and "They Can't Take That Away From Me" were taken from 1937 radio broadcasts. Because Holiday was under contract to a rival record label, she made no studio recordings with the band during their year together.

Conscientious care was taken with the sound, cleaned up from original 78-rpm recordings from the Smithsonian vaults and private collections. A well-illustrated, exhaustively annotated booklet by pianist and jazz historian Mark Tucker includes performers, recording dates, a detailed meditation on each song, and back-of-the-book bios on all the singers and soloists.

Once upon a time in New York, life was a cabaret. Or, at least you could find all the elements of life in a cabaret song.

The handsomely-packaged "The Erteguns' New York: New York Cabaret Music" crystallizes the after-hours glamor, elegance, decadence of the small, smoky boites du nuit. Atlantic Records President Ahmet Ertegun assembled 99 representative performances by 19 cabaret singers he admired over the years, and the collection conjures up the lost New York of urbane clubs like the Cafe Carlyle, El Morocco and the Stork Club, a glittering galaxy centered in the Broadway district.

The set opens auspiciously with a full side of Mae Barnes, and she's a revelation. When she ruled the Bon Soir in the '40s and '50s it was nicknamed the "Barnes Soir." She's particularly delightful on special material like "(I Ain't Gonna Be No) Topsy," a comically indignant protest about the kind of roles Barnes was being offered, written for her by Irving Berlin. Now in her eighties, Barnes is living in Long Island and should be designated a national treasure herself.

Sonorous Sylvia Syms creates an atmosphere of faded elegance on "Paradise" and "Down in the Depths on the 90th Floor." Joe Mooney applies his soothing tones to "Lush Life" and "Crazy She Calls Me." With his easy phrasing, Ted Straeter sounds like he's grinning when he sings "What's New" and "All in Fun," backed by a guitar-led rhythm section. Chris Connor graces seven songs like "The Night We Called It a Day" and "Moonlight in Vermont" with her foggy, oboelike tones.

The legendary Mabel Mercer rates 11 selections -- a full side and a half. Mercer's poised elegance and refined diction made her sound like a society dame -- albeit one with a slightly wicked sense of humor -- and she was at her best with a Cole Porter lyric like "Just One of Those Things." Mercer was one of the few who could put across a novelty like "Did You Ever Cross Over To Sneedens."

Bobby Short, who is still prolifically bouncing and beaming (Atlantic released the four-record compilation "50 from Bobby Short" (Atlantic 81715) early this year), is also well-represented with 11 songs, and his placement after Mercer is no coincidence -- Short is Mercer's male counterpart, as he proves on polished, extroverted versions of "Sand in My Shoes" "Slumming on Park Avenue" and "Flying Down to Rio."

The record turns the blue spotlight on the instrumental soloists for awhile, with selections from pianist Cy Walter and guitarist Eddie Condon. The set is sprinkled with live tracks that provide the ambience of cabaret: Behind Jimmy Lyon's piano on "Easy To Love," you can hear the clatter of diners and the club's phone ringing.

The last disc focuses on latter-day cabaret, with sensual Carmen McRae and Mel Torme', orchestral settings. Torme winds up the tour, doing his "Velvet Fog" thing on five tunes inextricably linked with the idea of New York.

The recording quality is superbly clean and immediate throughout. The disc is available on six records or as a three-disc CD set, both of which include an informative booklet with flavorful bios of the artists and a foldout map of the New York cabaret district.

Bobby Short has been doing some musical rediscovery of his own. "Guess Who's In Town: Bobby Short Performs the Songs of Andy Razaf" (Atlantic 81778) is a glossy set showcasing the black lyricist who penned the words to some of our most durable standards.

Short is sweet-voiced and precise within the late Phil Moore's lapidary, jazz-tinged arrangements, which put the focus on the words. "Honeysuckle Rose" gets an intriguing new rhythmic interpretation, and Short delivers a convincingly pained "How Can You Face Me?" and a spry, sprung "Ain't Misbehavin.' " He sparkles on songs from the "colored musicals" of the '30s, including "Tan Manhattan" and the poignant "Black and Blue." The evocative, allusive orchestration and vocal on "Make Believe Ballroom," the title theme of the WNEW radio program, brings back echoes of the era: "Away we go, by radio, to realms of sweet delight."