"It's literally classic rock 'n roll, not like disco which is from a very distinctive period. And of course all the other elements, like the elements of folk in 'Simple Song', that's back in vogue too, if you think of Norah Jones," she added, referring to the song that is the signature tune for the mass celebrant, whose crisis of faith is the piece's main event.

CLASSIC ROCK 'N ROLL

That seems very long ago, post 9/11, post Iraq war, post-paedophile priests and post a score of other calamities that Bernstein, who died in 1990, didn't live to experience.

In addition to penning three symphonies, several ballets, choral works and art song, Bernstein wrote "West Side Story," one of the greatest Broadway musicals, full of hummable tunes.

"'Mass' is really a synopsis and summation of Bernstein's philosophy of offering aspect and inclusion and sort of a big embrace to as many people as possible," she told Reuters in a telephone interview from Amsterdam, where she had just conducted a Brahms "Requiem" with the Royal Concertgebouw.

Alsop thinks "Mass" does all of Bernstein's works at least one, and possibly several times, better. She thinks of it, in fact, as his masterpiece, combining the best of everything he had in him, from traditional symphonic writing to 12-tone rows to liturgy to Broadway razzmatazz to plain old rock 'n roll.

This weekend, audiences in London will have a chance to decide whether Bernstein's mammoth opus for orchestra, rock band, marching band, soloists, three choruses, dancers — 500 people in all — is a musical hotch potch, as some critics said at the premiere in 1971, or an infrequently performed jewel.

With "Mass," Bernstein stacked the odds in his favor, not only with the number of people involved, but also by writing it so amateurs and professionals could perform it, side by side.

For these performances, Southbank has engaged Britain's National Youth Orchestra, Brazil's Youth Orchestra of Bahia, Iraq's National Youth Orchestra and America's Sphinx Organization of black and Latino musicians, to name a few.

"When I first did the piece in the '90s it sounded a lot more dated to me than it does today because we're in more of a retro mode now," she said.

But for Alsop, the piece still works, even politically.

"I think 9/11 would have been a rallying cry for him," she said.

"When the Berlin Wall came down he was there, with his Beethoven 9th and his orchestra from around the world, changing the wording to 'freedom' instead of 'joy'," she said,Ed hardy hats, referring to his 1989 concert celebrating the demise of the barrier between East and West Berlin, where he meddled with the wording of Schiller's "Ode to Joy."

"He was a guy who was at the center of every major political occurrence and I think that he would not only be horrified by the scandal in the Catholic Church, but I think it highlights his distress over organized religion — he hated blind belief, and he wanted everyone to question and probe."

Alsop, who is the first woman conductor of a major American orchestra, and has signed up for another five years with the Baltimore Symphony Orchestra,Calvin Klein, suggests people come with an open mind, an open ear, and let Bernstein's "Mass" do the rest.

"I think all of his music is quintessentially him," she said.

"He was an incredible and masterful storyteller and every piece he wrote has a deeper story."

(Marin Alsop conducts "Mass" at Royal Festival Hall July 10-11, http://www.southbankcentre.co.uk/; her recording of "Mass" with the Baltimore Symphony Orchestra is available on Naxos 8.559622-23)

American conductor Marin Alsop, who will lead two performances on Saturday and Sunday, July 10 and 11, at Southbank Centre's Royal Festival Hall, is a firm believer.

LONDON (Reuters) – Leonard Bernstein's "Mass" is the musical equivalent of the late American conductor and composer's bear-hugs and kisses on the lips: if you like emotional excess you'll love it, if you don't, you won't.

"That was always his goal — to involve as many people in this art form as possible."

Bernstein, who was famously taken up with left-leaning causes during his lifetime and had the posthumously published FBI files to show for it, used "Mass" as a platform to take aim at organized religion, the Vietnam War and authority in general.

Students from the local community will be singing, alongside professionals, and the performers' average age is under 20, Southbank says.

It might have a whiff of amateur hour, but Bernstein, ever the canny composer, would never let that happen.

What might seem dated about "Mass" is its political message.