`LOST WORLD' BOOSTS 12-YEAR-OLD'S PROFILE; SEEMING MATURE NOT A PROBLEM FOR CHESTER WHEN BLOCKBUSTER'S ADULT STARS ACT LIKE KIDS.

Byline: Bob Strauss Daily News Film Writer

Vanessa Lee Chester plays the designated youngster in ``The Lost World: Jurassic Park.'' But on the set of Steven Spielberg's latest dinosaur blockbuster, there was no question as to who was the real adult.

``I felt like I was the most mature person there,'' says Chester, who at 12 is a veteran of ``Harriet the Spy,'' ``A Little Princess,'' ``Honeymoon in Vegas'' and TV's ``Sesame Street.'' ``Everybody on the set was like a big kid.

``Vince Vaughn and Jeff Goldblum are the biggest troublemakers, I swear,'' she says of two older (in years anyway) ``Lost World'' co-stars. ``They were always trying to get gook from the dinosaurs in my hair, tripping me in the mud, telling me there were snakes around.

``And you should have seen Vince and Julianne Moore fight! It is so funny, it's like, `I don't like your orange hair, Julianne,' `Well, you have a big head, Vince'! She would go, `Vanessa thought she'd be working with adults. She was so wrong.' ''

Maybe because they were so silly, Chester became good friends with most of her co-stars. Especially Goldblum, whose daughter, Kelly Malcolm, she plays in the film.

``Jeff's cool; I wouldn't mind if he was my dad,'' says Chester, a former New Yorker who now lives near Universal City with her mother and 7-year-old brother. ``We both knew that we had to act like I was his daughter, that it had to be natural, so we got together before we actually started filming the movie. We went to Jerry's Famous Deli, we went to Toys R Us and he bought me some toys. We played basketball, even though he won because he's so much taller than me. We visited some of my friends, who went, `He was in ``Independence Day!'' Oh my gosh, Vanessa!' ''

Many have asked why Goldblum's Ian Malcolm would have an African-American daughter in the movie. Chester was one of the first to raise the question.

``I remember I was getting fitted for my wardrobe when they told me,'' she says. ``I was like, `No way! You've gotta be kidding.' I was surprised, but I really didn't care. I just thought, `Well, I guess I'm an interracial kid now.' ''

``Lost World'' screenwriter David Koepp explained how the unusual casting came about.

``In the book, there are two children, a boy and a girl, and they are students of a character that's not in the movie,'' Koepp says, referring to Michael Crichton's sequel to his best-selling ``Jurassic Park'' novel. ``We condensed them into one character, Kelly, and made her Malcolm's student. But I was having a terrible time making that work; why would he be teaching kids?

``Writing scripts is about connecting, and the movie is about parenting and nurturing. So I figured this should apply to the human characters as well as the animal ones, and I made her his daughter. Then Steven (Spielberg) said, `Shoot, I really wanted to cast Vanessa, I like her so much. But she's black and Jeff's white.' Then, sort of at the same moment, we both said, `Perfect, just leave it, it's great!'

``We live in a world where all sorts of different people are together,'' Koepp notes. ``Steven has adopted two African-American kids. I like it, it's unusual, it's interesting. You always want something interesting and different.''

Chester agrees. ``It says it's OK,'' she figures, ``it's OK to have a white father and a black child, especially in a movie that's got a major evolutionary theme.''

As for what's sure to be a quantum leap forward in her own star profile, Chester is, typically, maintaining a very mature perspective.

``I can't really associate myself with being a celebrity,'' she says. ``People pointing and whispering, `She was in ``The Lost World,'' ' I just don't get that. But if it does happen, I just have to accept that that's a part of acting. I can't be snobbish, that's not cool, and I can't be mean to fans because then they won't like me anymore.''

Grown up as she may be, Chester sounds just like anyone else her age when it comes to summer vacation.

``Man, I can't wait! I'm going swimming, I'm going to the movies, I'm going shopping with my friends. We've been working out every day so we look good in our swimsuits.''

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Photo: Initially cast as a student of Jeff Goldblum's ``Lost World'' character Ian Malcolm, actress Vanessa Lee Chester, 12, kept the part when the character was instead made his daughter.