When Frank Sinatra joined Tommy Dorsey and His Orchestra in January of 1940, he was an almost total unknown.

True, he had spent a little over a year singing with the Harry James band, and his version of "All or Nothing at All" with James enor- mously impressed those who heard it. Trouble was, that group was a little too select to do the young singer much good; at that point in its history, the James band was barely getting by.

So when the 24-year-old singer first took the stage with Dorse and company, few in the crowd -- or, for that matter, the band -- expected much. As Jo Stafford, whose group the Pied Pipers was singing with Dorsey at the time, recalled later, "Frank was very thin in those days, almost fragile-looking. When he stepped up to the microphone, we all smirked and looked at each other, waiting to see what he could do."

Then the skinny kid opened his mouth. "I know it sounds lik something out of a B movie, but it's true: Before he'd sung four bars, we knew," Stafford continued. "We knew he was going to be a great star."

In fact, Sinatra was a sensation with Dorsey. Even though h spent just over two and a half years with the band, Sinatra together with Dorsey put more than a dozen records into the Top 10, including such chart-toppers as "Dolores," "There Are Such Things," "In the Blue of the Evening" and "I'll Never Smile Again," that last spending 12 weeks at No. 1.

Each of those hits can be found on "The Song Is You" (RC 66353, five CDs or cassettes), a 120-song set that compiles all Sinatra's studio recordings with Dorsey, plus four tunes credited to Frank Sinatra and his orchestra, and more than two dozen live performances culled from Dorsey's radio broadcasts for NBC. (The set arrives in stores Tuesday.)

As a testament to the team's vitality, "The Song Is You" is hard t top. Not only is the sound remarkably good, with a fidelity and presence that belies the age of these recordings, but the quality of the work is remarkably consistent. It hardly matters whether the music is as classic as "Blue Skies" or as corny as "Indiana in July" -- there's a sense of discipline and musicality to these recordings that makes even the most forgettable tunes worth hearing.

Some of the songs, of course, will be instantly recognizable t anyone familiar with the big band repertoire. There are plenty of Sinatra-identified hits, like "I'll Be Seeing You" and "Polka Dots and Moonbeams." But there are also a number of Dorsey standards that were remade with the singer, such as "Stardust," a 1936 instrumental hit that was reconfigured in 1940 for Sinatra and the Pied Pipers, and "Marie," which is offered here in a sassy live version that smokes the more familiar Jack Leonard rendition.

But there's also a fair amount of material that seems silly b contemporary standards. It's hard to listen to lyrics like "She's a snootie little cutie/ She's a pert little skirt" (from "Snootie Little Cutie") without snickering, and even tougher to endure "I'll Take Tallulah," what with rhymes like "Oh that gal Tallulah (He's

Tallulah's fool-ah)."

Yet as goofy as that stuff got, somehow Sinatra found a way t make music out of it. It wasn't just a matter of staying on pitch and delivering the lyrics with a modicum of conviction; what keeps "Snootie Little Cutie" and its ilk from devolving into fluff was Sinatra's total devotion to the discipline of melody -- what the critic Henry Pleasants called "the seamless line" that allowed Sinatra to stitch the individual phrases of a song into a cohesive whole.

Given the context, it's easy to draw parallels between Sinatra'singing and Dorsey's trombone. Dorsey, after all, was one of the most strongly melodic players of his day, whose warm, burnished tone and elegant, legato phrasing came as close to crooning as any instrumentalist could. Moreover, the fact that Dorsey preferred playing in his instrument's upper register meant that his trombone possessed many of the same tonal qualities as Sinatra's light, smooth baritone.

Dorsey's use of vibrato is also instructive. Even though there was an undeniable sweetness to his sound, Dorsey never went in for the sort of wide, exaggerated vibrato favored by

the society band trombonists of the time. Instead, he used it lightly and sparingly, often holding back a moment in order to add a bit of dramatic shading to the note -- a trick Sinatra also used, and used well.

For his part, the singer has credited Dorsey's breath control a being an inspiration. "He would take a musical phrase and play it all the way through, seemingly without breathing, for eight, 10, maybe 16 bars," Sinatra wrote in a 1965 article for Life magazine. "Why couldn't a singer do that?"

It's not hard to find examples of how Dorsey's dulcet sound was reflected in Sinatra's singing, from the melancholy refrain of "Fools Rush In (Where Angels Fear to Tread)" to the jaunty cadences of "Let's Get Away From It All." Even more telling is the way Sinatra's phrasing becomes more liquid and expressive with each track, as if we're literally listening to him grow.

But the biggest surprise is how quickly Sinatra's artistic personality comes into focus. Spend time with the first disc, recorded during Sinatra's first months with the band, and what comes across is the wide-eyed, earnest quality of the singing. Skip to the fifth disc, where there's a live rendition of "Marie" recorded later that same year, and the transformation is astonishing.

As Will Friedwald comments in his liner notes, the arrangement's use of a jivey counter-vocal by the band is meant to convey the sense "that he's square and they're hip. But when Sinatra moves up to the mike, he's not just hip, he's immediately hipper than all of them put together."

Of course, we all know that now. But to hear that as it came across some 54 years ago, when America's music fans were just beginning to sense the greatness in this man's voice -- well, that alone is worth the price of this set.

FRANK TALK

What:Frank Sinatra concert

When: Monday, Aug. 29, 8 p.m.

Where:Merriweather Post Pavilion

Tickets: $100, $75, $50

KACall: (410) 481-7328 for tickets, (410) 730-2424 for information

LISTENING IN

To hear excerpts of "The Song Is You," call Sundial, The Sun's telephone information service, at (410) 783-1800. In Anne Arundel County, call (410) 268-7736; in Harford County, (410) 836-5028; in Carroll County, (410) 848-0338. Using a touch-tone phone, punch in the four-digit code 6158 after you hear the greeting.