For McCartney, It’s Not Easy Being Green : Pop music: The ex-Beatle, once idolized for his smile, has quietly emerged as a champion of environmental causes, using his music and fame to pack concert halls and deliver the message.

Paul McCartney, the activist?

The former Beatle pauses, as if trying the once unlikely image on for size during an interview moments before the start of his first U.S. concert tour since 1990.

For years, the late John Lennon was the former Beatle most associated with social activism.

Paul was always the cute Beatle, the romantic Beatle, the conciliatory Beatle--and the image stuck as he evolved in the ‘70s from rock ‘n’ roller to family man.

Rather quietly and dramatically, however, McCartney and his wife, Linda, have become outspoken advocates in recent years for environmental issues.

Those concerns are an integral part of the new tour, which began with an emotionally charged 2 1/2-hour performance here Wednesday at the Sam Boyd Silver Bowl stadium.

The tour includes a 6:30 p.m. stop tonight at the Hollywood Bowl, where McCartney will headline the National Earth Day Concert, before moving on Saturday to Anaheim Stadium.

“The strange thing about activism is it’s not easy,” McCartney, 50, said backstage at the stadium following the band’s sound check.

“It’s so much easier for me to go off and hibernate with my money, but I’m now an older guy, one of the planet’s elders almost . . . and I figure there is a sort of responsibility to either just tell everyone to ‘tune in, drop out, turn on, man,’ if that’s what you think, or to give them some ideas.”

In his case, the information to concertgoers includes a free, 100-page program that outlines the work of three social action groups endorsed by the McCartneys: Greenpeace, Friends of the Earth and People for Ethical Treatment of Animals.

The concert also begins with a 10-minute film that combines footage of McCartney’s career with scenes of animals being killed or tortured for commercial or research purposes.

Parts of the footage about animal mistreatment are so strong they cause some members of the audience to gasp or turn their heads.

In one of the most disheartening sequences, an elephant is electrocuted during a demonstration by Thomas Edison to illustrate the power of his discovery, electricity.

About the scene, McCartney said, “You go, ‘Well, I know where Edison’s head was at: “Let’s show them how powerful this thing is. Let’s even bring down an elephant.” ’

“And . . . the footage (treated it) like a great accomplishment. But now, it looks sick . . . horrific.”

McCartney’s activism isn’t just relegated to the souvenir program or the film. Early in the show here, he performed “Looking for Changes,” an angry attack on animal cruelty that appears on his latest album, “Off the Ground.”

The language of the song and the tone of the film are closer to the aggressive, anti-war stance of Lennon in the late ‘60s and early ‘70s than traditional McCartney--and McCartney worries about appearing too strident, thereby alienating much of his audience.

McCartney, who retains that disarming smile that once melted the hearts of millions of Beatles fans though his hair has long been streaked with gray, describes his approach to social involvement as “gentle activism.”

Even in the Beatles, he said, he tried to keep a balance between his personal beliefs and the music.

“There was always this idea that we could say it in our songs. . . . We could suggest it in ‘Let It Be’ or ‘Blackbird’ or whatever. We could plant these seeds without overtly becoming activists.”

McCartney recalled a conversation with an activist friend during his recent tour of Australia and New Zealand.

“I said, ‘We are playing to 60,000 people tonight. If I was just an activist, we’d be playing to 6,000 if we were lucky.’

“That’s what happens. The audience dwindles. It becomes more hard-core. You may become more high-profile, but you can lose your effectiveness, and that is the thrust of why I occasionally may appear to have straddled the fence. . . . But it’s not straddling the fence, very far from it. I don’t think anyone can actually look back and say the Beatles were straddling the fence.” This gentle activism has worked wonders for Concerts for the Environment, the group sponsoring tonight’s Hollywood Bowl concert, whose lineup also includes Don Henley, k.d. lang, 10,000 Maniacs and PM Dawn.

(The four-hour concert is scheduled to start at 6:30 p.m., and fans are being urged to use park-and-ride services to help reduce traffic congestion around the Bowl. For information call (213) 850-2000.)

Michael Martin, executive director of Concerts for the Environment, said McCartney’s involvement has helped move the National Earth Day Concert “to a new level.”

The wide demographics of his fans--all the way from teen-agers to Beatles lovers in their 50s--have been enormously helpful in getting media attention, both reports on the concert itself and a greater number of radio and TV stations willing to carry public service announcements.

And what about McCartney’s future?

One thing for sure is that he won’t do a formal farewell tour.

“At 50, doing this tour, I can see that it might be a farewell tour, but I wouldn’t want to announce it,” he said. “In fact, I don’t think in those kind of terms, farewells . Besides, they never work, do they? They’re always saying farewell and they’re back the year after. . . . It always seems like a joke.”

At the end of the interview, McCartney pauses as he heads toward his private dressing room.

“You know that whole thing about saying farewell is strange, because there are times when it’s so much fun that you feel like a kid again . . . happy just to be up there on stage. It’s hard to believe all these years have gone by.”