WITH "YANKEE DOODLE DANDY" playing in the background, Billy Joel, wearing a black suit and shirt, wanders with long, slow strides onto the MGM Grand Garden Theater stage in Las Vegas. After a few waves to a cheering audience, the Long Island native turns and gestures across the stage.

Out of the darkness, to a tune only the British would recognize, waggles the round-nosed and bespectacled Elton John. Dressed in a bright yellow leather suit and red cowboy boots, the 48-year-old piano master is displaying a touch of his flamboyant past.Standing in front of two 9-foot black grand pianos, Joel and John acknowledge the crowd's greeting. John turns to the gray-bearded piano man across the stage and bows. Joel responds with a salute. With signs of mutual respect now given for almost three decades of cranking out one piano hit after another, it's time for the two musical legends to get down to business.

Without a word the two sit at their respective stools, look over the ivory keys, face-to-face, and tickle out "Your Song" - John's signature tune. The two singers alternate verses and give a double-dose of piano. Before doing the same with his hit "Honesty," Joel turns to the screaming audience and sums up what every John/Joel fan feels.

"Now is this a cool idea or what?"

The cool idea popped into Joel's head two years ago. He wanted to put together the dream team of piano, kind of like Michael, Larry and Magic hitting the hardwood together. After all, the media has compared the two for years as the kings of keyboard.

"I've wanted to work with Elton for a long time and now it has finally come together for us," Joel says in the concert program.

John was receptive to the idea, but because of busy and conflicting schedules the tour took more than a year to put together. Joel was busy with his "River of Dreams" tour and John was working on "The Lion King" soundtrack.

"You don't turn down the opportunity to tour with another great piano player," John said.

THE TOUR HAS been worth it, both to the two performers and their fans. While tours by the Eagles and Rolling Stones have garnered the attention from morning talk shows, news telecasts, television shopping networks, MTV and VH-1, the John/Joel tour is quietly and slowly becoming one of the most prolific in music history.

The two piano pounders began the tour last summer on the East Coast, playing to 21 sold-out stadium crowds. Performance magazine awarded the tour its Tour Package of the Year. Concert Pulse ranked it as the top 1994 summer tour, grossing nearly $2.9 million per stop and averaging nearly 63,000 fans at each show. The John/Joel "Face to Face" tour resumed March 22 at Jack Murphy Stadium in San Diego and will end 11 shows later with concerts April 13 and April 14 at Joe Robbie Stadium in Miami.

Compared with other superstar tours, the John/Joel tour is reasonably priced. With the exception of the two Las Vegas shows, the only indoor stops on the tour, tickets are normally priced below $50. Fans basically get two concerts for the price of one.

The tour's success is not surprising - just look at the duo's credentials. Billy Joel's 15 albums have sold more than 50 million copies over 25 years. Most of his albums and singles have ended up atop the charts. He's won dozens of music awards, including six Grammys.

Since debuting at the Troubadour Club in Los Angeles in 1970, Elton John has been the most productive pop artist in music history. He's the only artist ever to have a top 40 hit for 25 consecutive years, surpassing Elvis Presley, who did it for 23 consecutive years. His 30 albums have sold more than 100 million copies. In 1971 he had four albums in the top 10 at one time. A member of the Rock 'n' Roll Hall of Fame, John recently won an Oscar and a Grammy Award for the "Lion King" hit "Can You Feel the Love Tonight."

On the footsteps of Jerry Lee Lewis and Little Richard, John and Joel are the ones who finished bringing the piano-playing vocalist to the forefront of rock 'n' roll. With the exception of Bruce Hornsby's one-year dethroning attempt, the two have ruled piano rock 'n' roll since the early '70s.

But while the media have painted a picture of rivalry between the two artists, John and Joel say it doesn't exist. They've even talked and joked about the comparisons. The two have a close camaraderie and mutual respect for each other's work. And both got most of their inspiration from the same source - the Beatles.

"We had a mutual admiration society," Joel told the Boston Globe prior to a concert at Foxboro Stadium. "Every time we'd see each other I'd say, `Oh, I loved it when you did this.' And he'd say, `Oh, I loved it when you did that.' "

THEIR SHOW BEGINS with three duets, after which Joel departs to "see ya later." John and his band play alone for about 90 minutes, broken up by a 5-minute solo performance by Ray Cooper, the peculiar mad scientist-looking percussionist who can play every instrument, including the coconuts off "Gilligan's Island." Joel returns once during the show's first half to join John in a rendition of "I Guess That's Why They Call It the Blues."

After a short intermission, Joel returns with his band to perform 11 songs. John, now wearing a bright green leather suit, returns once to join Joel for a duet performance of "My Life." Each performs a tribute to the other by playing one of the other's songs. John performs "New York State of Mind" and Joel does "Goodbye Yellow Brick Road."

"It's natural to have two piano players trade riffs and sort of see how each other's style melds," Joel said. "Our styles are different, but we can play similar to each other as well."

Joel is more "The Entertainer" and more personal with the audience, straying from the piano during several songs to dance and twirl the microphone stand like a baton. John stays at home, devoting his performance to piano-playing mastery by adding key-pounding solos to most songs.

The encore is what everyone paid good money to see, the two performing eight songs together. They even honor their predecessors with renditions of "Great Balls of Fire," "Lucille" and "A Hard Day's Night." Almost four hours and 37 songs later, the concert ends with the most fitting song, a duet performance of "Piano Man."

The two performers' moods are evident in the show. Joel, who's been on the road since his world tour began in September 1993 and has faced public scrutiny in his divorce from supermodel Christie Brinkley, is obviously exhausted. But fans can tell the tour with John is rejuvenating. Still, Joel says his world touring days are over when the concerts with John are finished. He plans to devote most of his future to writing and composing.

On the other hand, John's new life is written all over his face. Having overcome drug and alcohol addiction and fresh off his success with "The Lion King" soundtrack, John performs with the same enthusiasm he displayed in the '70s. He leaves little doubt that his music is the thread that's held his life together the past three decades, and he's having fun.

When the John/Joel tour is over, John will embark on a world tour of his own to promote his new album "Made in England." The tour will start in Europe and return to the United States in late summer. A spokesman at United Concerts said the company is trying to lure John for a fall concert date in Salt Lake City.

Now the bad news for those who didn't travel to Las Vegas to catch the duo perform: Joel's spokeswoman in New York says no albums, singles or videos are planned from the concert tour.