Q. "I need your advice on how to keep my 2-year-old boy busy during a long plane flight from here to India, which is almost 16 hours' flying time. He is a very active boy and does not like being cooped up inside. Even at home, he loves being outdoors. He likes to be on the move and he wants to do things himself. "I am afraid he will want to push the food cart in the plane and might annoy the stewardess and the co-passengers. "i do plan to take some books, puzzles and toys along with me. How else can I keep him busy and interested?" A. You want to prepare well -- and expect little. An active little boy is not going to behave like an adult, no matter how ingenious you are. But he But he can act like a happy little child, most of the time.

It's not a question of keeping him busy and interested -- it's a question of keeping both of you busy and interested. If you're bored, or angry, you can bet he will feel the same and if you feel cooped up, so will he. "inside" is a state of mind.

According to one of our favorite young mothers, it's the "wow, are we going on a great adventure!" that makes the difference. She found the plane ride can be as exciting to a 2-year-old as the destination, but you have to promote it.

A knapsack was also a big help. Her 2-year-old daughter packed her own for the family trip to Austria, but she had to be able to carry it herself.

After some experimental walks around the house, she whittled her load to these essentials: two bears, a small truck, crayons, a coloring book, toothbrush and tooghpaste.

She also was allowed to take a lunch-box, which was filled with a sandwich, a banana, small boxes of raisins, peanuts, mints and various other treats, but she had to carry this too -- and so she did. The child who is given responsibilities will act much more responsibly.

These parents brought other treats in their carry-on luggage, doling them out every hour or so as parents have always done on trips, and this helped too. o

Another parent who once traveled a lot with young children said she not only brought presents, but she wrapped them like treasures, even the boxes of raisins. Small things matter a lot when you're 2.

Airlines can be helpful, too, if you ask -- and this is no time to be proud.

Call them to reserve a bay of airline treats for children; special meals Although they don't always get delivered); extra fruit and small cans of pure fruit juice, since caffeinated sodas may keep him awake.

Also ask the airlines for a window seat, preferably by the bulkhead that divides the first and second class. The floor space is bigger here. In this country these seats usually are given to the first arrivals, but overseas airlines often assign them to families with young children.

Don't count on the airline, however, to provide a stroller, but you can take your own folding one aboard with you. It's a big help if you have to cross a large airport, especially if your child is sleepy.

You also need to take a damp sponge in a plastic bag and 1-2 changes of clothes. Even though you will clean your space every hour or so, a 2-year old gets mighty grungy.

Once aboard, your child will want to experiment with everything and to fight attendants give the kind of evil eye every parent dreams of -- but he can play in the aisle if the seatbelt sign isn't lit; if he doesn't clutter the floor with toys; if the cart isn't in the way, and if he doesn't get rotten looks from other passengers. If he does, the only trips he takes will be to the loo and back with you.

The attendant will help a little bit on any trip, but on such a long one she will have time to take your son for walks when you need to be alone. And if you ask (and perhaps if you don't) she will take him forward to watch the pilots in the cockpit for a few minutes.

This still leaves an awful lot of time. Some of it will be spent sleeping, of course, but most of the time he'll be snuggled in your arms and listening to lullabyes when he gets tired, and crawling in your lap and playing with toys when he's not. No activity will last long -- 10 minutes would be reasonable -- but if the toys and books are well-chosen and if you offer something new before he's quite bored with the old, they are going to be pleasant, if lively, minutes.

The best toys have the fewest parts, which is why you don't take puzzles. Even at home the pieces seem to have a life of their own, always disappearing into crevices you never knew were there, but in a plane it's almost hopeless.

Stick with crayons and coloring books; the old-fashioned "slate" where a child writes with a stylus and lifts the pliofilm to make the picture disappear, and the Matchbox cars he drives up and down the folding table in front of his seat.

A slim version of a Sears catalog is good too, for your child can tear out the pictures of things he likes -- with help from you -- and file them in his lunchbox.

The books that will entertain your child best will have some activities built into them and some of the best can be found at the Cheshire Cat, the children's bookstore at 5512 Connecticut Ave. NW.

He'll like the flaps and surprises in the small H. A. Rey paperbacks, like "Anybody at Home?" (Houghton Mifflin $1.75); pop-up books like the series on shapes, colors, numbers and opposites by Larry Shapiro (windmill, $2.95) and "The Magic Blanket," one of a series by Stella Farri (Harper & Row, $4.50) and Tom Blazer's lovely "Eye Winker, Tom Tinker, Chin Chopper" (Doubleday, $1.95). The 50 musical finger plays entertain a child all the better if you take some hand or finger puppets with you.

This trip will be taxing for both of you, but it still will be an adventure, so long as you expect it to be.