All through the school year, you looked forward to going to camp. You thought about how much fun it would be to go swimming, to hike in the woods, to share a cabin with new friends, and to eat marshmallows around a campfire.

Now the day for going to camp has finally arrived. Your bag is packed. Your name tags are sewn in your T-shirts. But instead of feeling excited, you find yourself wishing that you could just stay home with your family and forget you ever volunteered to go to camp.

If you start having feelings like this, you may think there's something the matter with you. There isn't! Almost everyone, including grown-ups, experiences anxious feelings when they're about to start new things. Teen-agers going away to college feel nervous about it; so do grown-ups who are about to begin a new job, or older people preparing to retire.

It may help to remind yourself that the nervous feelings you've got aren't unusual. Ask your parents, your brothers and sisters, or your friends. They'll probably tell you that they have often felt that same way you're feeling right now.

So you get on the bus, and go off to camp. When you get there, things are really busy. You meet your cabin mates and your counselors. You discover where the swimming pool is, and you eat your first camp meal. Hey, you think, this isn't so bad after all. Camp is fun!

But when night comes, and you're lying in your bunk again, you may start to feel kind of homesick. You may miss your familiar bedroom, your pets -- even that creepy older brother who teases you all the time. You may start wondering if the other kids are going to like you.

Dr. Nick Long is a child psychologist at American University in Washington, D.C. He studies how children feel about their experiences. "All kids worry about whether they will fit in at camp," says Long. "It's important to remember that you're not the only one feeling that way."

People often feel strange, lonely and sad for a couple of days when they're in a new place, Long explains. "It's difficult to leave behind what's familiar, safe and predictable for a whole new situation."

It will take you a little while to get used to camp routines, and to make new friends. But once you do that, you should feel fine.

There are a few things you can do to make the adjustment to camp easier. Long suggests visiting the camp and meeting the staff before you go there for the summer. That way, you'll already know what the place looks like, and you'll recognize a few familar faces when you get there.

Make sure that you go to a camp that has activities you enjoy. If you love softball, it probably isn't a great idea to go to a camp where all you'll be doing is practicing the violin. If you adore the violin, you probably won't feel very comfortable at a camp where all you'll be doing is rock-climbing.

There are hundreds of camps with many different programs to choose from. Some camps teach farming; others teach survival skills. Some teach you to be good sailors, others to be good actors. Your camp should fit your personality and interests.

"I went to camp in North Carolina last summer," say Elizabeth, age 10. "At first I felt awful. I missed my parents and my house and my dachshund. I missed being able to go to the refrigerator for a snack whenever I felt like it. But after a few days it started to be a lot of fun. I did a lot of stuff I'd never done before. I even learned how to rapel down a cliff on a rope. It was the perfect camp for me. When I left, I cried. Now I miss the friends I made there. I can't wait to go back this summer."

You and your family can get information on camps and their programs from the Advisory Council on Camps, 174 Sylvan Ave., Leonia, N.J. 07605, (201) 592-6667. Tips for Parents

Psychologist Nick Long advises parents to be sensitive to their children's reaction adjustments to camp. Don't ridicule their feelings, or tell them not to act like babies. If you get that "I hate it here" call, remember that your youngster will probably tell you his or her worst feelings. Things may not be nearly as bad as they sound. Even so, don't depend on a youthful counselor's appraisal of the situation. Consult with senior staff member about your child.

"If that sad, lonely call comes, you might respond by saying, 'I'm glad you called, I'm glad you can tell me how you're feeling. Tomorrow we'll talk to the counselor about it,' " says Long. "That gives your child a sense of linkage between home and camp."

Most homesickness problems evaporate quickly. But there are times when the camp-child fit just isn't right. "If your child has been at camp for five continuous days, hasn't formed one significant attachment, and is very oppositional, then it may be time to make the decision to leave," says Long.