When Keith Coogan was an adolescent, he was offered the role of Tom Sawyer in a cable television version of the classic Mark Twain tale.

Coogan, now 21 - he has been a professional actor since he was 5 - didn't have far to look to find someone to discuss the role with. His grandfather, the late Jackie Coogan, played the Twain character in the first Tom Sawyer film ever made.After giving his grandson a few tips on how to play the character he portrayed in 1931, the elder Coogan passed on a few more words of wisdom that are still being used by the young actor, one of the stars of the action film "Toy Soldiers."

"He didn't give me acting lessons or anything like that, but what he did give me were conduct lessons," Coogan said. "He taught me how to conduct myself on the set. He taught me to keep my mouth shut and my eyes open.

"He said that nobody wants to hear what a kid has to say, so he told me not to mouth off all the time but, instead, to save up what I had to say until the time was right, and then firmly and clearly state what I wanted to say. Then people had to listen to you."

Apparently, Keith Coogan took his grandfather's advice to heart. People are listening to him.

"Keith is not only an extraordinary actor," said "Toy Soldiers" writer and director Daniel Petrie Jr., "but he's got a real sense of rightness about the characters he plays.

"We ended up throwing away what the script said about his character in this film and going with what Keith felt the character would be like. He knew what the character would wear, how he would keep his cigarettes, what he would have in his pockets, how he would walk . . . just everything.

"He has a definite opinion about acting and he's usually right. He's a smart kid."

In the movie, which could be described as part "Taps" and part "Die Hard," Coogan is a student at a prestigious prep school that is being overrun by murderous Colombian terrorists.

It is the second of three films that Coogan is starring in this year - "Book of Love" was the first, and his next will be "Don't Tell Mom the Babysitter Is Dead" - and in each, he displays a natural flair for comedy.

"I enjoy making people laugh, but eventually I would love to play the leading-man roles," Coogan said. "But I'm not exactly a beefcake right now; I've got a little bit of a gut, I'm losing my hair and I'm counting my chins.

"If I take care of my body, I could end up with leading-man roles, but it looks now like I'm probably going to end up looking a lot like Uncle Fester," he said with a laugh, referring to the odd character made famous by his grandfather on the TV series "The Addams Family."

The Uncle Fester character was the last hurrah in a storied but tragic career that began when Jackie Coogan was 18 months old. At 6, he became an internationally known movie star when he appeared opposite Charlie Chaplin in "The Kid."

Within two years, the youngster was making $1 million a picture, and he amassed a fortune, only to see it squandered by his mother and stepfather. Eventually, he sued his family for the money, but by the time he won the case, only a fraction of the original fortune was left.

The case led to passage of California's Child Actors Bill, popularly known as the Coogan Act, which protects the income of child actors, including that of young Keith Coogan.

"You didn't have to tell anyone in my family how tough this business could be on child actors," he said. "My grandfather taught us that this is a real scary business and that your biggest enemies are your own weaknesses . . . and your family.

"My mom (Jackie's daughter) had seen so much of the bad side of the business that she once went to court to fight the Coogan Act so she could get more of my money saved than is required by law.

"Sadly, that law is really a law in theory, and kids still have to sue their parents. That's got to be the sickest thing imaginable."

Keith's mom didn't get along with her father, Coogan said. She had moved out of his house when she was 15. In the next two years, she married, got pregnant and divorced. As a result, Keith and his mother lived in near-poverty. At one time, they were living on welfare, he said.

When he started working in the entertainment business at age 5, they were residing in the tennis court changing room of a Malibu mansion. It had a bedroom and bathroom, he said. His mother cleaned the main house in the mornings and drove Keith to auditions in the afternoon.

"My mom wasn't crazy about the idea of me going into show business, given what had happened to her dad, but she was supportive right from the start," Coogan said. "I said I wanted to be on television when I was 5 years old, and she agreed to drive me around for the next 10 years. She was great."

He got an agent quickly (his mom became his manager and still manages him) and got his first job as a stand-in for another young actor in a MacDonald's commercial. The director of that commercial hired him to star in his next commercial.

Coogan appeared in dozens of television shows - he was on the series "The Waltons" for a full season - and made his film debut in the 1987 movie "Adventures in Babysitting."

"My grandfather was very proud I went into this business, and I'm only sorry that he died (in 1984) before I had a chance to show him my film work," said the young actor, who legally changed his name from Mitchell to Coogan to honor his grandfather after his death.

"For a long time, he was just my sick grandfather who moved in with us during the summer months," Coogan said. "Then, one day, when I was about 8, I got to see `The Kid.'

"I was blown away; I remember looking at the screen and saying: `Wow, that's Grandpa.'

"He was a great actor, and I think I learned a lot from him. I'm still learning from him. He impressed upon me just how important it was to keep working and not peak too fast. I think it all came too fast for him, and I don't ever want to peak in this business.

"I always want to work, so that's why I keep working on the craft of acting and don't worry about stardom. I just want to be an actor."