School has started again. You have classes to go to, and homework to do. There are new teachers to get used to, and new friends to get to know. Fall is a busy time.

You're in a new grade this fall. You probably have more independence than you did last year. Maybe your parents have decided that you're old enough to take the bus across town by yourself, or to come home to an empty house in the afternoon. On weekends, you may be allowed to go to a mall or the movies with your friends and no grownups.

All that independence can be exciting. But it can be a little bit scary, too. You may run into situations that are hard to handle. As you grow up, you have to learn to make important decisions about how to spend your time, and how to take good care of yourself.

One of the most important choices you can make is the decision to say NO to drugs and alcohol.

The National Institute on Drug Abuse reports that children in the United States have probably heard about drugs as early as fourth grade. The White House Drug Abuse Policy Office says that kids from fourth grade on, may feel pressure to try drinking or drugs. Has that happened to you?

Bruce Weitz, the actor who plays Mick Belker on "Hill Street Blues," is the honorary chairman of the national PTA's drug prevention program. He has received letters from kids all over the country. They write to tell him how worried they are about drug use. They say that they often feel pressured to try drugs and drinking, and wish that their parents and other adults would do more to keep dangerous substances out of their lives.

"I see some of my friends drinking or even smoking. Sometimes when my friends do this and I don't, it makes me feel out of the group," one 13-year-old girl wrote. "I wish I could talk to my parents, but I'm afraid of the way they'll react toward this."

When Beth, a fifth-grader in Washington, tried talking to her mom and dad about drugs, she was pleasantly surprised. They were much better informed and more helpful than she had thought they would be. They didn't get mad at all. They told her all they knew about the bad things that drugs can do. They told her that they trusted her to know enough not to try drugs. And they encouraged her to talk to them if she was worried about classmates who might be using drugs.

Beth's parents suggested that she say "No, thanks," if anyone offered her drugs. If someone says "Let's get high," they told her say no, but to offer to do some other activity instead. They told her to say "I know it's bad for me." And if the friends insist, Beth's parents said, they're not very good friends to begin with.

After this conversation, Beth felt much better. She felt like she had her parents' help and support.

The PTA and many other organizations have designed materials to help children and their parents communicate about drug and alcohol use. You can write to these organizations at the addresses listed below.

At school, you may be able to get involved in anti-drug activities or clubs. In the Washington area last spring, some 3,000 kids saw a mini-musical called "The Power of No." The play's message: It feels better, is healthier, more fun and cooler to be drug-free than it is to use drugs. The show will be performed in schools in and around Washington again this fall. To find out where, call Ronna Corman, the show's director, at 490-4115.

If you need help saying no to drugs, you might want to start or join one of the "Just Say No" clubs around the country. Last spring, more than 3 million kids took part in "Just Say No" walks and rallies all over the country.

Kids aged 7 to 14 belong to the Just Say No Clubs of America. Some of the people involved in the clubs are famous -- like Soleil Moon Frye of "Punky Brewster," and Nancy Reagan, the president's wife. Others are kids like you, and adults like your parents and teachers. Members of the clubs support each other in their decision to stay away from drugs, and they take part in many different activities in their communities.

If you want to find out more about the "Just Say No" clubs, you can call a toll-free number: 800-258-2766. The person who answers will tell you how to start a club, or how to join one in your area. "If you already have a club, let us hear from you," says Beth Schecter, who works with the clubs. "We will make sure you get mailings about our activities. We want to do everything we can to help you say no to drugs."Tips for Parents

For free information on how to talk with your children about drugs and alcohol, contact: The National PTA, 700 North Rush St., Chicago, Ill. 60611-2571; (312) 787-0977. National Clearinghouse for Alcohol Information, P.O. Box 2345, Kensington, Md. 20795; (301) 468-2600. National Clearinghouse for Drug Information, P.O. Box 416, Kensington, Md. 20795; (301) 443-6500. National Institute on Drug Abuse, 5600 Fishers Lane, Rockville, Md. 20857; 800-638-2045. Just Say No Clubs of America, 1777 North California Blvd., Suite 200, Walnut Creek, Calif. 94596; 800-258-2766. Catherine O'Neill is a contributing editor to the Health section.