An authentic jazz band version of George Gershwin's "Rhapsody in Blue," with Benny Goodman as clarinet soloist, sounds as if it should be the highlight of tonight's Wolf Trap concert on public television. But it turns out to be an acute and prolonged blooper.

The pianst, Patricia Prattis-Jennings, literally and very visibly trembles her way through the piece. The band, under the direction of Morton Gould, sounds as stodgy as any symphony orchestra that ever inflated the "Rhapsody" into a hot air ballon. Not even Goodman's opening arpeggio is as electrifying as one would hope.

But the one-hour program, at 8 o'clock on Channel 26, still has moments of musical reward, as Goodman and group swing through "The King Porter Stomp," "When Your Lover Has Gone," "Here's That Rainy Day" and "That's A-Plenty," among others.

In addition, the Wolf Trap series, one of the few in public TV to be produced by WETA, has undergone moderate alterations that improve the show. The nuisance of an on-camera host has been eliminated, replaced with "program notes" read by announcer Paul Anthony.

And Bob Blansky of Dolphin Productions created extremely attractive animated graphics to open the program.

While the Wolf Trap shows have expanded the musical variety available on television - and, says producer Ruth Leon, the programs, especially those on jazz and ragtime, are selling "very, very well" abroad - the fact remains that they have blazed no major trails in making concerts more visual for television.

In fact, director Stan Lathan approaches Goodman and crew as if they were distant deities with whom one dare not become involved. Lathan's favorite shot is a long one of the stage with the bottom half of the screen a big black puddle, where the unlit audience sits. This is wasted space, to put it mildly, and it helps keep the Wolf Trap shows from being top-notch in all departments.