It's good to be Gad Elbaz, an ultra-Orthodox singer whose cool sound, stage swagger and good looks have won him legions of young fans. But it is also difficult, for reasons embodied by Etti and Rachel, two giggling teenagers who pressed up against the backstage gate at a concert here last week hoping to catch a glimpse of the 23-year-old pop idol.

"He is so handsome," gushes Etti, 17, whose ankle-length skirt and turtleneck sweater fit the modesty requirements of the ultra-Orthodox dress code while the pink accents and "Abercrombie" insignia suggest she is not immune to the dictates of fashion. "He's also good and sweet."

Rachel, 16, nods. The two, who didn't want to give their last names for fear of angering their parents, have driven two hours from the coastal city of Netanya to see Elbaz perform, and the barrier required at all ultra-Orthodox concerts to separate men and women could not keep them from reaching the male-only backstage area. Asked where their parents were as the two snaked past security guards, Rachel offers a nonchalant flip of her hand.

"Oh, we left them at the Western Wall," she says, referring to the holiest place where Jews pray.

There are thousands of Ettis and Rachels in Elbaz's life -- problematic if necessary elements of his unique stardom and of Israel's changing ultra-Orthodox society.

Elbaz appreciates the fans who made his recent album a top seller, attend his shows by the thousands and request his music with such frequency that his popularity has crossed into Israel's secular world, where religious devotion is generally considered uncool.

But the e-mails calling him a "world-class hunk," the frequent phone calls pledging love and the adoration visible at his shows have put Elbaz in hot water with some of Israel's most powerful rabbis. They fear the Elvis-like effect he is having on the young female portion of the highly traditional community, known as Haredi, where song is considered nearly as powerful as prayer.

The ultra-Orthodox establishment does not quite know what to make of Israel's first Haredi heartthrob. Is this happily married man who studies the Torah four hours a day a threat to their insular world? Or are his balladeer's voice, hip two-day beard, and pious lyrics a way to preserve Old World traditions in the age of Britney Spears?

"There is an audience and a crowd that will always stay the same and never change," Elbaz says after finishing a radio show in which every caller was a woman. "But I think it's all right to be modern, and that's what's happening in our world."

Elbaz is a compact, energetic presence. His olive skin and dark eyes reflect his family's North African roots. He wears a simple black kipah, the skullcap of religious Jews, and performs in black suits and white shirts open at the neck.

An estimated 700,000 of Israel's nearly 7 million people identify themselves as ultra-Orthodox, a fast-growing, mostly poor population that holds Jewish law above the secular state. As a result, many secular Israelis resent the benefits the Haredi community receives from the government, which include living stipends, tax breaks and exemptions from mandatory military service.

In recent years, Haredi rabbis have begun encouraging young men, many of them full-time yeshiva students, to enter the workforce to ease the financial strain on their traditionally large families. The community is gingerly engaging mainstream Israeli society, a dislocating trend of which Elbaz is a part. (The term Haredi refers to the entire ultra-Orthodox community, including Sephardic Jews of North African descent, like Elbaz. The Hasidim are a large segment within the Haredi that generally traces their roots to Eastern Europe.)

Without sanctioned movies, television or Internet, music is the Haredi world's chief form of entertainment, magnifying the importance of people such as Elbaz.

"What there is left to us are these singing events," says Rabbi Yehuda Deri, a member of the Chief Rabbinate Council of the State of Israel. "But this can cause problems because they are places boys and girls meet together, and 10 years of religious education can go down the drain."

Elbaz's popularity and Deri's fears collided last summer in Beersheba, a city in southern Israel where Deri has been chief rabbi for seven years. Elbaz sold out the city's thousand-seat hall after posters around town declared that the rabbinate had officially approved the show. But no one had consulted Deri, a mistake attributed in the heated aftermath to the concert promoter.

Using the popular religious radio stations, Deri urged fans not to attend the show. Elbaz canceled the concert, calling it a misunderstanding. But because of similar criticism that has dogged many of his shows, Elbaz and others suspect the music itself was the problem.

"The problem is that if you don't sing the 'oy, oy, oy' of the old Hasidic music, the next thing you hear is, 'Oh, don't go to his show. He's not religious,' " Elbaz says. "But if we were still playing this old music, our teenagers would be leaving religion to go out and find something new.

"What this rabbi didn't realize," Elbaz continues, "is that I am a role model. I can influence them not to make mistakes."

The show was held a month later after Deri's rabbinate coordinated the event. It began with a warning that any inappropriate behavior -- that means you, young ladies -- would mean instant cancellation. Boys and girls used separate entrances and watched the show from opposite sides of a barrier. Deri, who did not attend the event because of his daughter's engagement celebration that evening, received updates by cell phone.

"It's totally possible to be a popular singer on the Haredi street and maintain the boundaries of Jewish law," says Deri, who worries that the shows could lead to prohibited physical contact between unmarried men and women or cause exuberant young women to violate the rules on modesty. "Okay, maybe the girls won't jump all over him if this is followed correctly. But he will still be just as popular."

Elbaz began performing at age 4, mostly duets with his father, Benny, a successful secular singer who found religion when Gad was a boy.

While attending religious schools as a teenager, Elbaz began developing a style that draws on Arab rhythms, hip-hop beats, the harmonies of the Backstreet Boys and the ballads of Whitney Houston and Celine Dion. Jewish law generally prohibits men from listening to women sing; Elbaz said he received dispensation from his rabbi to do so.

"He gave me the power to make you dance," run the lyrics to his biggest hit, "Tonight Is the Night." "Open your hearts, disengage from all. Believe in yourself, believe you are mighty." Of his three solo albums, "Meanings" has had the most success, selling about 80,000 copies since hitting Haredi music stores last spring. That ranks him among the biggest-selling Haredi music stars, whose store sales benefit from lack of piracy among devout fans. But those figures, as well as the popularity of his video clips on Israel's version of MTV and the fact that his songs are featured in karaoke bars, mean a fair number of nonreligious Israelis are also fans.

Ariel Berman, a disc jockey at the ultra-Orthodox radio station Kol Hai, has witnessed the evolution of Haredi music from the bouncy Hasidic songs of older generations to a genre that includes boy bands, rap and alternative rock groups. He has also fielded a number of questions about Elbaz from concerned religious leaders.

"I tell them Radio Kol Hai is an alternative to nonreligious stations and that Gad Elbaz is an alternative to Madonna," Berman, 24, says during a chat in the station's no-frills Tel Aviv studio.

Moran Elbaz, 19, was once among Gad's many fans. Now she is his wife, chief lyricist and mother of the couple's year-old son, Benjamin. The two met after Moran organized an Elbaz concert near her home town of Holon, where the couple now live. They married after a short courtship conducted by telephone and under the watchful eye of a grandmother.

Now Moran finds herself fielding a steady stream of phone calls from young female fans, who often hang up once she asks the reason for the call.

"The fact he is religious makes it easier because there are limits," Moran says. "The secular world is unrestrained and shameless. With us, it's more subtle. I don't care if he has girl fans. It's his crowd, and he makes his living from it."

On a cool recent evening, a line of men and women winds down a hillside path toward a stage in the East Jerusalem neighborhood of Silwan that is the site of archaeological findings dating to King David's rule. The frantic rhythm of Hasidic rock, heavy on the horns, echoes through the narrow valley.

Halfway down the slope the path forks -- women going in one direction, men in festive fur hats to celebrate the Sukkot holiday going the other. Under a thatched shelter backstage, Elbaz sips coffee with Mordechai Ben-David. At 54, Ben-David, known as MBD, is a superstar of what he describes humorously as "Hasid rock," which sounds something like the ska band Madness singing the Psalms.

"We have our own Taliban," Ben-David says of the criticism Elbaz has received. "But I think this trouble he's having with the rabbis is good for him. He knows he's being watched."

After a rollicking set by Ben-David that has his sidelocks twirling, Elbaz takes the stage. A crowd of men stretches before him as he begins a peppy pop song celebrating the Second Temple, destroyed by the Romans in A.D. 70. Some young men sway to the music; others join hands to dance in large circles.

The women remain out of sight behind a series of dividers more than 100 yards away. They watch Elbaz on a screen, many of them smiling broadly at his image and the sound of his clear, powerful voice in the chilly night air.

After his three-song set, Elbaz pauses to sign an autograph for Etti and Rachel, just before the two girls are whisked away by security guards amid mounting complaints from the male audience nearby.

"Tell Gadi Elbaz we're lovesick over him," Etti says over her shoulder as she is escorted back to the women's section.

Gad Elbaz performs in Jerusalem, above left, where the audience was segregated by sex, above. At left, Elbaz chats backstage with "Hasid rock" star Mordechai Ben-David. Rabbi Yehuda Deri, right, fears that "10 years of religious education can go down the drain" if boys and girls were to interact at concerts.