Dave Lambert, Jon Hendricks and Annie Ross sang with a crispness, a bright upness that sounded so '60s, so Camelot, so Rat Pack. From 1958 to 1962, they were the hip thing. The trio's tunes trumpeted that America could do anything, even add rapid-fire lyrics to the great jazz solos and make them swing as song.

And then Ross dropped out--drugs, they said. And then Lambert died--car crash. And Lambert, Hendricks and Ross--L,H&R to the cognoscenti--became a moment, a marker in the lives of those who found love or wisdom or the right path while under the influence of three singers who put words to bebop and called it "vocalese." (Vocalese, first made popular by Eddie Jefferson in the '40s, is not scat, a wordless voice taking a turn as jazz soloist, but a blend of song and instrument, original in its lyrics yet exactly true to a previously recorded solo.)

Thirty-six years passed. Now, Hendricks and Ross are singing together once more, proving that the past can return, and the right time for this past is now, because when America is rich and happy, it likes its songs fast and chipper and faster and swinging.

Hendricks is 78 now, Ross 70, yet the two--appearing tonight at the Kennedy Center--are right in tune with the swing revival and the neo-lounge movement. Cocktails, Gap khakis, swing numbers on WHFS--it's now, baby.

Hendricks and Ross laugh it up at a Foggy Bottom cafe, finishing each other's sentences as all partners are supposed to do. But for all those years apart, while they conducted solo careers, they rarely spoke. "The important thing is the music," Ross says, deflecting a question about the dynamic between the two. "That's the real truth."

Whatever tensions there once were, last year's reunion was launched like a high-tech start-up: boom. Or so it looked. Actually, the return, like the duo's music, resulted from a mix of choreography and serendipity. The scene was Birdland in New York, 1998, Ross on the bandstand, Hendricks in the audience, having just "dropped by." Truth be told, the two singers had had a couple of vague talks about getting back together, but what happened next could not have been planned: When Ross invited Hendricks onstage to join her in her finale, Count Basie's "Jumpin' at the Woodside," the room burst into a roar. Standing O, before they sang a note.

"People were running out the door, trying to buy those little instant cameras, trying to record a bit of jazz history," Hendricks recalls.

"It was pandemonium," Ross remembers. "Thrilling."

Ross returned the favor, visiting a Hendricks gig at the Blue Note. Getting back together was a no-brainer now.

That's how it had seemed back at the beginning, too. So easy, so right. Hendricks, a minister's son who quit law school to devote himself to writing lyrics and playing drums, had been putting words to some Count Basie numbers. Hendricks joined Lambert, a former tree surgeon; and Ross, a child actress turned singer with Lionel Hampton's big band; and they hired a choir to record an album of Basie tunes. It was awful beyond words. They scrapped the choir and overdubbed themselves as trio. Was less ever more.

They were the right thing at the right moment. Hendricks, the distinctive one with a taut velvet tone. Ross, providing the range and clarity. Lambert, the deep foundation. They were rigorous enough to be taken seriously by jazz purists, cool enough to win over the likes of Miles Davis and Charles Mingus.

The jazz greats could be a jealous bunch, proprietary about their innovations, suspicious of anyone purporting to build on their work. And here were these singers copying every single note and inflection of the giants' solos. The potential for disaster was huge: They could play the notes but lose the soul, they could capture the feel but add words that twisted the meaning.

From the first playback, they knew they had avoided the pitfalls. Ross remembers that "I had taken a little tape recorder to the studio, and I went home and called Miles and played it and said, 'What do you think?' "

Davis told her to hang on, and he yelled to the visiting Mingus to pick up the extension, and they all listened "and they just went crazy," Ross recalls, like it was yesterday.

All part of jazz history now. What jazz has become is something uncertain--parts still very much alive, but other parts preserved as a museum piece, pasteurized into the non-music called smooth jazz, or surviving as the subject of college courses and nonprofit institutional bands.

And so, even as the greats die off almost one a week--Nat Adderley, who played cornet, just last week; the survivors talk about funeral fatigue--there is a passion for finding connections to the years when jazz really mattered.

The connection, Ross says, "is the swing. That's the thing we have. When we're singing, it's bliss."

Which is why the two had tried once before to get back together. In 1985 they reunited, replacing Lambert with another singer, Bruce Scott, who was chosen for his vocal similarity to their late partner. Some critics liked the trio fine, but it never felt right to Hendricks and Ross.

Hendricks resumed his solo singing act.

Ross went back to her acting career, including her most memorable role, as Tess Trainer, the drug- and drink-ravaged jazz singer in Robert Altman's "Short Cuts." Like Ross, Tess's voice was coarsened by time and abuse, yet still a rich instrument. Like Tess, Ross--a show-biz lifer who was born to Scottish vaudevillians and appeared in "Our Gang" shorts in the '30s--had overindulged; she faced health problems, bankruptcy, periods of unemployment. Her stardom with Lambert and Hendricks was bookended by affairs with jazz drummer Kenny Clarke and comic Lenny Bruce. But again, like her movie character, Ross emerged from her troubled years wiser.

If Ross is reticent about her life beyond the music, Hendricks is the opposite--still electric in a blazer of shocking blue. He's busy setting up an Australian tour, and they're both writing lyrics for Dizzy Gillespie tunes they plan to record later this year.

"It's like translating a novel," Hendricks explains. "You listen to the notes again and again and find the words that make the closest sounds in English. And then you find a story to link the words. The title of the song gives you the subject matter and then each horn becomes a character, commenting on his place in the drama."

Sometimes the lyrics hang together; often, they fly by so fast, you hardly have a chance to do anything more than cop a mood from them. Yet Hendricks and Ross have kept every line in their heads all these years.

Some adjustments were necessary. Here and there, they shifted keys to accommodate older voices. "I don't hit those G's over high C's anymore," Ross notes.

This time, they dispensed with a third singer, divvying up some of Lambert's old lines and giving the rest to Hendricks's guitarist, Paul Meyers. The result, many critics say, is an ensemble feeling, a spirit that emerges untarnished by the decades of separation.

"The guitar is so close to the human voice, Jon and I can hear Dave's voice while we're singing," Ross says. "It's almost a subliminal thing. People come up to us after the show and say, 'I heard Dave.' "

Those are the older fans; the younger ones take it for what it is now, fresh and fast.

Jon Hendricks and Annie Ross appear at the Kennedy Center tonight at 7:30. The concert is sold out, but extra seats may be added. Call 202-467-4600 for information.

CAPTION: Annie Ross and Jon Hendricks, part of the landmark '50s jazz trio, revive their partnership tonight at the Kennedy Center.

CAPTION: Annie Ross and Jon Hendricks, reunited: "When we're singing, it's bliss," she says.