Los Angeles ? When Britney Spears walks on an arena stage to face 20,000 sets of adoring eyes and the dual sensory shock of having thousands of young female voices screaming her name at a decibel level that could wake the dead, accompanied by enough flashbulb-induced energy to light a Midwestern state, she says that only one thought comes to mind:

“I can’t believe that all these freakin’ people have come to see me.”

The pop princess says it without a shred of irony. She is serious. At a moment like that, all she can think about is how lucky she is to be Britney Spears.

“I find it interesting that they find me so interesting,” she explains. “I have tried to figure it out, but I haven’t a clue. I would really like to know.

“If I had to guess,” she adds in a little-girl voice with a thick Louisiana accent, “I suppose they see that I love what I do and that I’m just like them. Kids can sense that.”

Well, not exactly like them.

Britney she has passed into that rarified stratum of stardom where one name suffices is sitting comfortably at the top of the show-business heap right now. Her first three albums all debuted at No. 1, her Pepsi commercials are everywhere, her movie, “Crossroads,” hit theaters recently and she sets fashion trends for an entire generation of young girls.

But, make no mistake; being a pop icon can be exhausting. Take last week, for example.

It included three days of nonstop promotion in New Orleans to hype her movie, a stop at the NBA all-star game in Philadelphia and an appearance the next day in Burbank on “The Tonight Show.”

She arrived at the NBC studio at 10:30 a.m. to join her band and backup singers, who already had been rehearsing for a while. Britney and her backup singers were required to sing all or part of her new hit single, “I’m Not a Girl, Not Yet a Woman,” at least a dozen times while technicians worked on the sound. Each time, the singer dutifully repeated the lines without a complaint.

When the sound was deemed perfect for that night’s performance, she escaped to a second-floor dressing room. She is tinier, and perhaps even prettier, than you might expect from what you see on television. She is not a giddy schoolgirl but considers each question thoughtfully, although she occasionally erupts into a spontaneous giggle.

She is wearing a trendy hat, a simple blouse and hip-hugging blue jeans tucked into ornate Western boots. Her famous midriff is bare, of course. She is wearing several rings, including one with small diamonds on that all-important finger of her left hand. But she insists that she and boyfriend Justin Timberlake of the band ‘N Sync are not engaged. Or married. Or having sex.

Outside the dressing room sits a very large, and ever-present, bodyguard, who can be seen in most of those recent paparazzi photos of Britney on vacation in Hawaii. There was Britney, Justin and her bodyguard walking into the ocean in Hawaii. There was Britney, Justin and her bodyguard walking out of the ocean in Hawaii. There was Britney, Justin and the bodyguard having a grand old time.

“I don’t even think of him as a bodyguard,” she says. “We’ve been together four years, and he’s just one of my friends who I hang out with.

“And I don’t always need a bodyguard,” she adds with a hint of defiance. “I sneak out for pizza at 3 in the morning all the time.”

A skyrocketing star

Born in Kentwood, La., young Britney took to performing early. By the time she was 9, she already had appeared in an off-Broadway show. Two years later, she was living in Orlando as a member of the Mickey Mouse Club at Disney World. She and Justin met as Mouseketeers, and soon after shared their first kiss.

In 1998, she released her first album, “Baby One More Time,” which sold an astonishing 21 million copies, and followed that with a second album that sold 17million copies. The third album, “Britney,” sold 746,000 copies the first week alone. She has written a couple of books with her mother, Lynne, has hosted “Saturday Night Live” twice and now has set her sights on Hollywood.

“Crossroads,” directed by Tamra Davis, is based on an original idea by the singer about three childhood friends who set out on a road trip. Britney’s character wants to meet her biological mother and ends up singing in a talent competition in Los Angeles.

David Gale, an executive producer on the film and senior vice president of MTV Films, said the music network has been trying to get Spears into films for three years.

“We saw something in her during her early videos, long before she became the biggest pop star in the world,” he said. “She seemed to have the ability to transfer that charisma from her music to the screen. Unfortunately, her career took off, and she was not available to make a film.

“What she has that so many other music stars don’t have is that ability to connect with an audience on a personal level. So many music stars are difficult and brooding, but Britney is not standoffish in any way. To her fans, she has always been the girl next door, the best friend or the big sister. That’s a rare quality that doesn’t come along that often.

“If you don’t believe me, look at all the Britney imitators. They don’t seem as natural as her, and that comes off to an audience as fake.”

A reluctant role model

The singer said she is serious about her acting career but admits she has a lot to learn.

“It is such a challenge because I’m not a pro at it,” she said. “It’s not like what I feel like when I’m singing or dancing. I know what I’m doing then. But it’s exciting doing something I’m not that good at yet.”

If the film seems tailor-made for Spears, with a few musical numbers and a standard story about a good-natured young woman and her best friends, that is no accident.

“I’ve looked at a lot of scripts the last few years, but I never want to do movies that I’m not prepared for,” she explained. “I guess I’m a little bit of a control freak when it comes to that. I like to know what I’m doing. If I’m going to work this hard on something, I want to be passionate about it.

“When an actor is passionate about a role, you can see that on the screen.”

The singer said her movie, which includes a love scene, has an important message for her young female fans.

“I have the same three best friends I had in day care, and I thought everybody was like that. I was surprised to find out they’re not,” she said. “I think it’s important for young girls to see that kind of friendship. There’s no need for girls to be envious of other girls.”

Although she said she never wanted to be a role model, she knows she has an impact on young girls. And that is one of the particular reasons she said she wanted to get that message of friendship across in her film.

As for the parents of her fans who are concerned about her impact, particularly when it comes to wearing sexy clothes, Spears suggested that they lighten up.

“If I had a little girl who was into Madonna, and every night she put on a Madonna outfit, I would think that was so cute,” she said. “I’d say to my daughter, ‘Baby, you can’t wear that out to the grocery store, but if you want to play dress-up with your friends, that’s OK.’

“That’s all I’m doing; I’m playing dress-up, only I’m doing it on stage in front of a lot of people.”