BY DAVID KRONKE >STAFF WRITER

"The Sisterhood of the Traveling Pants 2" is actually based on the fourth (and final) book of Ann Brashares' beloved series about four close friends who spend their summer vacations from school apart, connected by a magical pair of jeans they swap back and forth.

A couple of story lines from the second and third books are mixed into the new film, but Brashares and the actresses who play her characters have mixed feelings about not being able to bring the entire series to life.

"Ann did an amazing job of tapering the girls' growth over these books, and I do wish they had been given more time to breathe rather than everything squeezed into one movie," says America Ferrera, who reprises her role as Carmen, who's about to become a stepsister in the second film.

"It would've been nice to take our time and go through each book," agrees Alexis Bledel, whose character, Lena, gets a shock when she returns to Greece in the new film. "We're getting older, though, and I don't think they could've done it fast enough. It's fitting that the story is told while we still look young."

On the other hand, Amber Tamblyn, who plays the rebellious but withdrawn Tibby, says with a shrug, "It could be either way. This is a great film. It would've been great to make four films, but it would've been impossible, because our schedules are much more difficult to work out."

For her part, Brashares is diplomatic. "I think purists in the readership might be confused," she says, "but why that decision was made was a pretty sensible one. It was not an option to make four individual films, but the fourth book was the clear end of the story, and we wanted to get to that point. So once you enter into that thinking, it makes sense."

The first "Sisterhood" was a modest box-office success in 2005, but strong DVD sales spurred the sequel. "The sequel options were about to expire, and they put this one together quickly," Bledel explains.

In the new film, Carmen heads to Vermont, where she finds herself auditioning for a role in a play. Tibby is in New York, finishing up a film-school assignment, though her attentions are diverted by a pregnancy scare. Bridget (Blake Lively) goes to Turkey for an archeological dig before detouring to Alabama to meet the grandmother she never knew.

And Lena goes to art school in Rhode Island, where she is romanced by a fellow student, until a problematic turn of events returns her to Greece, the home of the ex-boyfriend for whom she still has feelings.

Carmen, Tibby and Bridget head to Greece to help Lena out.

Which may have been a little plotting by committee: While making the first film, the actresses lobbied Brashares to write an installment that brought the four friends together in Greece.

"The first time around, we came up with all these ridiculous ideas to get them together in Greece," Ferrera says.

"They wanted all four of them to go to Greece," Brashares says. "That was definitely by popular demand."

"It's the best idea," Lively enthuses. "We were really happy that that happened, though once we got there, it was more Jason Bourne-like than `Sisterhood'-like. We had these moped accidents in our first scene."

The actresses were tooling along on their mopeds when they turned a blind corner, "and we crashed and stacked up," Lively reports. "I was on crutches the rest of the time, which took away from the excitement of walking up those beautiful cobblestones."

During production on the first film, the actresses became friends as close as their characters. While shooting the second film, the other women helped Lively prepare for the first season of her TV show, "Gossip Girl," by offering advice on working in series television (each of the others have their own shows on their resumes: Ferrera on "Ugly Betty," Bledel on "Gilmore Girls" and Tamblyn on "Joan of Arcadia") and helping her find an apartment in New York from an Internet café in Greece. Back in Manhattan, Tamblyn helped Lively paint her new place.

"We're actually strangely very close - I felt like we were being paid to hang out," says Tamblyn, who notes that she has very few other friends who are actors.

"It was hard to get us in character, because all we want to do is make each other laugh," Lively says. "We don't want to turn that off, even when we're doing lines. It might be unprofessional, but it worked. They (the film's director and producers) actually encouraged that."

Brashares and the actresses acknowledge that the new film walks a tricky line in discussing sexuality for a movie whose target audience is young teens.

"That was a little bit of a quandary," the author says. "I know my readers are young, but the readers are growing up with the books. The fourth came out six years after the first. I did struggle with that, but by the fourth book, they're older. That's a big four years in a girl's life, from 16 to almost 20. I couldn't look past the characters to the readership. Who are they? What are thy realistically thinking about?"

"Ann does good job writing material that doesn't talk down to her audience, but takes their age into account," notes Bledel. "She deals with the emotional aspect of sex, not for the sake of entertainment, but handled in a responsible manner. Amber's story line is about not being ready to handle the situation. Definitely, with everything that kids are exposed to, this is appropriate for them. Brings things they've heard about into a relatable context."

"If you're 20 and not thinking about being sexually active, that's a little odd," Brashares continues. "If I was going to reflect that kind of life realistically, it meant there would be more sexuality. I didn't want it to be gratuitous but try to reflect who these girls are and what's important in their lives."

And ultimately, Tibby is supported by her friends.

"The strongest type of friendship is to give one another the power to face the world," Tamblyn says. "When you come together and deal with heartache and all the challenges, and that allows you to go on."

David Kronke, (818) 713-3638 david.kronke@dailynews.com

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