If the 20th Annual Manassas Jazz Festival had a minor theme, along with its celebration of the older forms of jazz, it was that a younger generation of fine players will carry on the tradition.

In session Friday evening through last night at the new Dulles Ramada, the gathering of about 50 musicians from here and abroad brought together players of long association, others who had never performed together and one local working group. There were structured sets devoted to Jelly Roll Morton and King Oliver and there were no-holds-barred jams. A cornet player from Sweden, Bent Persson, was impressive and moving with his Louis Armstrong sound.

Banu Gibson, a young singer from New Orleans, captivated with a program that included high-energy jazz vocals, double-entendre blues growled out Bessie Smith fashion and novelty numbers delivered in baby voice. An electrifying performer who combined poise, joie de vivre and ferocious swing, she was a festival favorite.

Clearly, the stars of the festival were the veteran players whose associations had included departed greats of jazz history. Max Kaminsky's trumpet, both clarion-open horn and "dirty" with plumber's-helper mute, fired several bands with the likes of "Royal Garden Blues." The mile-a-minute sticks of drummer Barrett Deems supplied the fuel for several sets and Johnny Blowers, Bunny Berigan's drummer in the late 1930s, was stunning on "Caravan."

Freddie Moore, at 85 years old the senior guest, delighted with outrageous mugging, vaudeville-era antics that included drumstick juggling and mock preaching. Don Goldie's trumpet, Paul O'Connor's trombone and Joe Muranyi's clarinet graced a number of ensembles.

Along with the visiting musicians noted above were some of the Washington area's finest players. Mason (Country) Thomas' full-bodied tenor saxophone and the assertive attack of Art Poncheri's trombone enhanced several combos.

Two preeminent interpreters of Jerry Roll Morton's piano works, "A Prairie Home Companion's" Butch Thompson and University of Michigan Prof. James Dapogny, at back-to-back uprights, offered four-handed versions of Morton classics, Gershwin tunes, a slow drag blues and, at one keyboard, a rumbling boogie-woogie number.

A trio comprising soprano saxophonists Jacques Kerrien and Tomas O rnberg, the one French and the other Swedish, and clarinetist Gary Gregg dug into the musical terrain of Sidney Bechet and brought it off in style.

The consistently high level of performance notwithstanding, a polished group of comparative youngsters, drummer Brooks Tegler's nine-member Hot Jazz, brought the crowd to its feet in ovation with its steaming hot renditions of swing-era materials. What more confirmation of the group's authority does one need than the delighted presence in its midst of former Benny Goodman guitarist Steve Jordan?