The creative artist must be familiar with the work of his predecessors if he wants to add to or change the direction of tradition. Jazz musicians -- no less aware of this need than those in the other arts -- have been looking back to the '20s and '30s with increasing frequency. Two recent releases illustrate the diverse approaches that can be taken.

Not a revival, but rather a fresh creative effort is the first album of the Widespread Depression Orchestra, nine musicians in their 20s who have apparently adopted as their creed the conviction that the '80s will see a second coming of the Swing Era.

So vital, relaxed, and authentic are their renditions of 11 numbers from the books of the Duke Ellington, Count Basie, Earl Hines, Jimmie Lunceford and other great black bands of the '30s that a blindfold test would leave even some experts unsure of the source and circumstance of the recordings.

There are two reasons for the uncertainty. First, while echoes of earlier players can be heard, each of these musicians has a distinct instrumental voice of his own. Clearly the influence of Cootie Williams can be detected in the plunger-mute trumpet rasps of Jordan Sandke, yet his vibrato has a cutting edge that is all its own. Again, the impact of Johnny Hodges on altoist Michael Hashim has been profound, but it is only a starting point for this talented 23-year-old who also has listened carefully to Charlie Parker. Similarly, Michael Le Donne has fashioned a pianistic identity out of Hines, Art Tatum, Bud Powell and others.

The second reason is the manner in which these vintage materials have been utilized. Passages have been interpolated, solos created, the arrangements rewritten. In short, the Widespread Depression Orchestra has made originals of the originals. For verification check out their feverish re-interpretation of the Ellington classic "East St. Louis Toodle Oo," leader Jonny Holtzman's wry vocalizing of Cab Calloway's "Reefer Man," the up-beat use they make of the Earl Hines Orchestra's "Comin' Home," or Billy Strayhorn's ballad "Day Dream" (a vehicle for Hashim). The album is on the Stash label (ST-203), which heretofore has specialized in reissues of materials which the Orchestra recreates.

Since jazz first came to public attention six decades and more ago, the oftheard observation has been that melody, (and, as the years went by, rhythm, the conventional chorus, harmonic structure, etc.) had been altered beyond recognition and comprehension. Now comes an album that could bridge the gap between the traditionalists and the modernists.

Despite their iconoclastic beginnings in the avant garde of the 1960s, Air (a trio of reed player Henry Threadgill, bassist Fred Hopkins and drummer Steve McCall) has taken a conservative approach in "Air Lore" (Arista 3014), which treats four classic compositions from the early years of this century. Of course there will still be raised eyebrows and some grumbling among the dinosaurs.

On Morton's "Buddy Bolden's Blues," Threadgill's plaintive tenor saxophone follows closely the original melody, then stretches out in a tumultuous improvisation over McCall's New Orleans parade drum press rolls. Hopkins walks slowly behind, darting into asides along the way.

Air's craft is nicely displayed on Scott Joplin's early piano dance suite "The Ragtime Dance," with Threadgill's staccato alto taking the part of the right hand, Hopkin's bass the left. Morton's "King Porter Stomp" makes good use of the composer's concept of the riff as "a foundation, like something you walk on." A nearly 12-minute "Weeping Willow Rag" is structurally faithful to the four strains of Joplin's composition. McCall and Hopkins take the first and third in solo, Threadgill the second and fourth with the rhythm support of his two co-workers.