As the athletes march into the stadium carrying banners and flags, the crowd cheers. The athletes wave and smile at their fans. Then they walk out onto the field and prepare to take part in the many different events planned for the day.

Sounds like the Olympics, doesn't it? Well, you're right -- it is the Olympics. But the participants in this Olympics aren't famous competitors like gymnast Mary Lou Retton or swimmer Steve Lundquist. They may be kids or adults you know -- members of your class at school, or your church, or people you've met in your neighborhood. They are Special Olympians -- mentally handicapped people who have been training hard for this exciting day.

You've probably heard about the Special Olympics, or seen some of its main events on television. All over the United States, and in many other countries, volunteer coaches and organizers hold Special Olympics competitions every year. Every four years, Special Olympians take part in international Summer Games or Winter Games. The next major Games will happen in the summer of 1987.

Eunice Kennedy Shriver, a sister of President John F. Kennedy, had the idea of starting athletic competitions for mentally handicapped children and adults. She thought that these special people would benefit from the exercise, and from the fun of competition. First, Mrs. Shriver ran summer camps at her home in Maryland. Then she got many other people involved. The first big Special Olympics happened in Chicago almost 20 years ago. The event showed people that retarded citizens could perform and compete like anyone else -- and have a lot of fun doing it.

The Special Olympics has grown and grown since then. Now over 1 million people all over the world take part in the athletic events every year. Mentally retarded people 8 years old and older can take part. They play many different sports, from track and field to gymnastics to cross-country skiing. Kids try their skills at basketball and Frisbee, volleyball and soccer, softball toss and bowling. Some Olympians swim in races; others race in their wheelchairs.

The Special Olympics organizers think competing in the events is just as important as winning. Their pledge is: "Let me win. But if I cannot win, let me be brave in the attempt."

That's what makes the Special Olympics special. Everyone wins, no matter who crosses the finish line first. Those athletes who do come in first win medals; those who participate receive ribbons, and lots and lots of praise.

For most of you, running in a foot race or swimming a 100-yard dash is no big deal. But for a mentally handicapped person running that race or jumping into the pool can be very difficult. It takes a lot of effort and a lot of courage to learn the skills needed to take part in the event. No wonder people cheer so loud when Special Olympians cross the finish line -- no matter how long it takes them to get there.

Have you ever heard of a New York Yankee named Ron Guidry? He's a great baseball player -- good enough to have won the Cy Young award, given every year to the best pitcher in each league. His award hangs in the living room in his Louisiana home. Next to it there's another award -- a gold medal from the Special Olympics. Ron's brother Travis, who is mentally retarded, won the medal in a softball throw event. Ron Guidry has said, "I believe it took more character and sheer guts for Travis to win his medal than for me to win the Cy Young award."

Athletes who take part in the Special Olympics need a lot of support. If you and your family want to get involved, there are a lot of things you could do. Are your mom and dad great soccer players? They could be certified as Special Olympics coaches. High-school age kids can also help train the Olympians. Junior high kids can be volunteer "huggers" -- supporters who stand at the finish line, cheer for the athletes and give them big hugs when they complete their events.

If you're not old enough to be a hugger, you can still be a Special Olympics supporter. "Be a fan," a spokeswoman for the Special Olympics said. "All those people out cheering in the stands do one of the most important jobs at the games." Tips for Parents

In 1988 the Special Olympics will celebrate its 20th anniversary. The volunteer organization's goal for that year is to recruit another 500,000 participants, bringing enrollment in the program to 1.5 million. If you're interested in involving your family as the anniversary year approaches, contact:

Special Olympics, International Headquarters, 1350 New York Ave. NW, Washington, D.C. 20005-4709; 628-3630.

In addition to its events for mentally handicapped people aged 8 and older, the organization runs a program called "Let's Play to Grow" for very young children. It's a supplement to Special Olympics as well as preparation for participation in the games. For information, contact the international office at the address above, or check with your local Special Olympics group.