''On the Line'' may be Lance Bass' debut as a leading man, but the 'N Sync singer appears to be making the transition from pop idol to thespian without much trouble. It's a chilly April day in downtown Chicago, and Bass' character Kevin, a shy adman desperate to track down a dream girl he encounters on the L train, has just spotted his soulmate at the Wabash and Adams stop. He bounds up the platform stairs to catch her. After two takes, Bass jogs over to Beth Flanagan, his personal assistant and childhood friend.

''Did you see the emotion in my steps?'' he asks, nudging his pal's arm. ''I did on the first take,'' she says, playing along. ''It was kind of overwhelming.''

Okay, maybe Flanagan's a bit biased -- after all, she's known Bass since she was 13. Still, America, prepare yourself: The 22-year-old singer might just be saying bye, bye, bye to being a teen dream and hello to becoming a Hollywood hyphenate. The $10 million romantic comedy, due Oct. 26, is not just Bass' first major film role (the IMAX hit '''N Sync: Bigger Than Live'' notwithstanding), it's also the first project from his 10-month-old production company, A Happy Place.

'''N Sync can't last forever,'' says Bass of his move toward producing. ''Hopefully, we've got another good 10 years ahead of us.... I just think with acting, there's not a time limit on it. That's why I want to get into this I love to entertain, and this lives forever.''

The 'N Sync guys have always roamed outside the boundaries of boy-banddom: JC Chasez wrote and produced for the girl group Wild Orchid; Chris Kirkpatrick has his skater-style clothing line, FuMan Skeeto; and Justin Timberlake dabbles in songwriting and acting (remember last year's ABC movie ''Model Behavior''?).

Bass and Joey Fatone -- who has a supporting role in ''On the Line'' as Kevin's rocker buddy, Rod -- are the movie geeks. In addition to writing treatments for 'N Sync videos, the duo once penned a script for ''Grease 3,'' though copyright issues kept that project from happening. ''God did not give me the talent to write [songs],'' says Bass. ''But I love creating movies.''

In January 2001, Bass funneled that cinematic passion into A Happy Place, a company created with Wendy Thorlakson (a former exec at Tom Hanks' Playtone) to bring musicians and athletes to the big screen. Initially, the company considered making an 'N Sync movie, but the guys were dismayed at the narrow options. The scripts ''were just cheesy,'' says Fatone. ''Five guys, bound for destiny, singing in a group. That's what we do in real life.''

Thorlakson kept digging, and beneath the heaps of teen fluff (like ''Mork the Dead Teenager'') she found ''On the Line.'' Deciding the ''hopeless romantic'' Kevin was ''exactly like Lance,'' she passed the script on to her partner. Bass was so enamored of the nice-guy role, he pitched the film to Miramax himself. ''We weren't looking for an 'N Sync vehicle,'' says Bob Osher, the studio's copresident of production. ''Obviously, [their] wanting to be involved adds to the project.'' (It helped that Miramax had also done business with Happy Place's coproducers, Tapestry Films, on 1999's ''She's All That'' and the current ''Serendipity.'') ''It's a romantic comedy for a younger audience,'' adds Osher of the PG film's appeal, ''but it also talks about friendship. There's a good moral to the story.''

Sure, once they scrubbed the script clean of the drinking, cursing, and sex. The original draft (by Eric Aronson and Paul Stanton) ''felt more like an R-rated movie,'' says director Eric Bross, whose credits include the Lauryn Hill indie ''Restaurant.'' ''But at the heart of it [was] this sweet idea. Still, we had to consider 'N Sync's audience.'' For a preteen-friendly rewrite, Bross enlisted David Wagner and Brent Goldberg, and out went the naughty words, a montage of Kevin's pals scoring with a bevy of babes, and one plotline that had Bass in a no-shirt-attached love scene. ''I had to start working out,'' he says. ''Then, three weeks before filming, we cut it. I was like, whew.''

After the cleansing, ''On the Line'' still needed a female lead. Enter Emmanuelle Chriqui, a Canadian-born beauty who got her break in a McDonald's commercial. ''At first I was like, well, you're sort of driving for career longevity,'' she says, asked if she was concerned about costarring in what will likely be dubbed ''the 'N Sync movie.'' ''Then I read the script, and it was so cute.''

The challenge then became to jam the shoot into a four-week window during which the band would also be finishing their album ''Celebrity'' and rehearsing for a 37-city tour. Over 33 days, Bass and Fatone bounced between Toronto and Chicago, filming by day, recording at night, and jetting off to L.A. or Orlando for photo shoots and rehearsals on weekends. (Fatone, 24, also took a one-week daddy break when longtime girlfriend Kelly Baldwin gave birth to their first child, Brianna.) ''It's been crazy,'' says Fatone, slumped on a couch in the Chicago Cubs' business office after shooting in Wrigley Field. ''I was [in Toronto] about two weeks, then I left. Then I went back again for three or four days, then I left.'' Pause. ''I think I went back there again.'' Pause. Sigh. ''And now we're here.''

At least the weary stars didn't have to deal with any ''Hard Day's Night'' scenarios. To throw fans off the scent, Bass used the alias ''Ted Geisel'' on call sheets and in hotels (''I'm a huge Dr. Seuss fan,'' he explains). ''It's been pretty tame,'' confirms Chriqui, 24. ''They're so normal, just regular guys. I forget they are the superstars of America.'' So have the sleepy commuters on the train platform, who are throwing bored glances at Bass as he waits to shoot a scene.

Finally, one woman approaches him with her daughter. ''Can you sign this? She can't speak,'' she says, nodding toward her bashful teen. Bass autographs her notebook with a flourish.

What's the biggest advantage of having a pop star produce your movie? Platinum-selling clout. ''He does solve a lot of problems,'' says Thorlakson. ''Things like, we're having trouble getting MTV -- Lance can say, 'Okay, let me get the president of MTV on the phone.''' And once the tour began, the band did its share of shilling: At each concert they screened a trailer and handed out free movie posters. 'N Sync have also provided two songs for the soundtrack, and, to top it off, Timberlake and Kirkpatrick filmed last-minute cameos (we won't spoil the surprise, but we can tell you Kirkpatrick does a mean French accent).

Despite all that, Bass says he won't use his pop-star status to promote the film further: He vetoed any ''starring Lance from 'N Sync'' references in posters, trailers, and TV ads. ''I really want this to stand on its own,'' he says. ''I explained [to Miramax] that our fans are not stupid. They're going to know that's me.'' The studio concurred. ''There really is a huge danger in going out and saying this is just an 'N Sync movie,'' says David Brooks, Miramax's cohead of marketing. ''That just narrows the film. Everybody agreed from the get-go, a little 'N Sync goes the distance.''

Whether or not ''On the Line'' is a success, it's clear Bass is hooked on Hollywood. He recently auditioned for the upcoming Reese Witherspoon comedy ''Sweet Home Alabama'' (he was deemed too young for the part), and A Happy Place has more projects in development (including ''Shooting From the Heart,'' a basketball drama based on an article by ''Tuesdays With Morrie'' author Mitch Albom). And fans of the WB's series ''7th Heaven'' may see Bass reprise his role as Beverly Mitchell's beu in future episodes. But Bass' ultimate Hollywood ambition is markedly less wholesome: He wants to die in a horror movie, ideally by Freddy Krueger's razored hand. ''The way I look at it,'' says Bass, ''half the people want to see me in a movie, and half the people want to see me die. So I think everybody will be happy.''