SUMMERTIME and the reading is easy. And a good book is just the thing to fill a long afternoon or shorten a car ride for the kids. Here are a few to try: ACTIVITY BOOKS

THE BERENSTAIN BEARS' MAKE AND DO BOOK -- by Stan and Jan Berenstain (Random House, 1984). This activity book has been designed with younger readers (preschool to Grade 2) in mind and will surely please fans of the ever-popular Berenstain Bears; $2.95.

THE BEACHCOMBER'S BOOK -- by Bernice Kohn (Puffin Books, 1982). This book is ideal for families who spend time at the beach. The suggested activities utilize all those beach "treasures" that children collect, and there's an appendix that identifies common shells and seaweed. % (FOOTNOTE)OR VERY YOUNG READERS (3 TO 6)

THE DOOZERS OF FRAGGLE ROCK -- by Jennifer Taubner (Holt, Rinehart and Winston, 1985). This board book is based on the hit HBO series that stars Jim Henson's popular Muppets; $2.95. A companion book by the same author is "A Fraggle Rock Party," $2.95.

MAX'S BIRTHDAY -- by Rosemary Wells (Dial Books, 1985). Max is a delightful bunny who, with his sister Ruby, has many fun-filled adventures. He's a popular character with young children; $3.50.

ANGELINA AT THE FAIR -- by Katharine Holabird (Crown, 1985). Angelina, the popular mouse, is back in another adventure. This time she loses her cousin Henry in the haunted house at the carnival; $5.95.

JELLY BELLY, ORIGINAL NURSERY RHYMES -- by Dennis Lee (Peter Bedrick Books, 1985). These absurdly funny nursery rhymes will tickle your funnybone. $8.95.

GRANDMA'S HOUSE -- by Elaine Moore (Lothrop, 1985). This gentle picture book is a must for any child who goes to visit grandma during the summer; $13. YOUNG READERS (7 TO 9)

HOT AIR HENRY -- by Mary Calhoun (Wm. Morrow & Co., 1981). This book was featured on the popular televised summer reading series, "Reading Rainbow." Henry is a very unusual Siamese cat who gets into extraordinary adventures, much to the chagrin of the normal human family with whom he lives; $6.95.

MISS NELSON HAS A FIELD DAY -- by James Marshall (Houghton-Mifflin, 1985). Fans of Miss Nelson will be delighted with this new book when Miss Viola Swamp becomes the school's new football coach; $12.95.

AMELIA BEDELIA GOES CAMPING -- by Peggy Parish (Green-Greenwillow, 1985). Anyone who has ever followed the zany antics of Amelia will chuckle as she goes camping for the first time; $8.95.

THE PATCHWORK QUILT -- by Valerie Flournoy (Dial Books, 1985). A warm story about carrying on family traditions as a young girl helps to complete a quilt her grandmother has started; $10.95.

BABE, THE GALLANT PIG -- by Dick King-Smith (Crown, 1985). A charming story of a pig who saves himself by learning to herd sheep; $8.95. OLDER READERS (10 AND UP)

COME SING, JIMMY JO -- by Katherine Paterson (Dutton, 1985). The newest book by Katherine Paterson tells the story of an Appalachian family who go from hometown recognition to big-city fame through their cooperative musical talents; $12.95.

THE RUNNER -- by Cynthia Voigt (Atheneum, 1985). This book is another story of the Tillerman family, focusing on the character of Bullet. Children who read Voight's previous novels of the Tillerman family will also want to read this one; $11.95.

CHINA HOMECOMING -- by Jean Fritz (Putnam, 1985). This is the sequel to Fritz's award-winning book "Homecoming: My Own Story," in which she discusses revisiting the country in which she was born; $12.95.

SILVER BURDETT PICTURE HISTORIES -- This is a series of new books on various ages of world history that fascinate older readers. Titles include "Castles," "Knights" and "The Musketeers"; $7.95.

THE TIME TRAVELER BOOKS -- is another new series published by EDC Publishing Co. These picture-type books take the reader back into time to visit the pharaohs, knights and ancient Romans; $4.95. RESOURCE BOOKS FOR PARENTS

GAMES TO PLAY IN THE CAR -- by Michael Harwood (Congdon & Weed Inc., 1983). This book provides ideas to entertain children of all ages and provides maps to help children understand the geography of where they are traveling; $6.95.

WASHINGTON! ADVENTURES FOR KIDS -- by Marti Weston, Heidi Simmons and Florri DeCell (Children's Innovations, 1984). This book provides learning activities for grade school children who are visiting sites in Washington, D.C.; $5.95.

THE WASHINGTON ONE-DAY TRIP BOOK -- 3rd edition, by Jane Ockershauser Smith (EPM Publications, 1984). This guidebook gives you 101 offbeat ideas for things to do and see in the Washington area; $7.95.

GOING PLACES WITH CHILDREN IN WASHINGTON -- 11th edition, edited by Salley Shannon and Ruth Ann Phang (Green Acres School, 1985). Undoubtedly the most well-read book by families who sightsee with their children; $5.95.(END FOOT)