We planned our strategy carefully. We'd get there early to be sure of being in the front of the line. Then, when the doors opened, Jeffrey and Linda would hurry over to the children's table and Carrie and I would check out the records. We'd also bring our own bags, the kind with handles that my mother used to call "shopping bags."

Once a month the Montgomery County Library System sells books, magazines and records at the Wheaton Library on Georgia Avenue; the sale, organized, operated and staffed strictly by volunteers, is a bookaholic's dream come true. For those who happen to be bargain-lovers as well, hardbacks sell for 25 cents each, paperbacks and magazines for five or ten cents each and records for a dime.

The basement room we and about a hundred other men, women, students and children poured into was filled with tables groaning under the weight of hundreds of books and magazines; paperbacks and more magazines and maps were stacked on the floor, and volunteers kept bringing out still more from huge stacks in the back room.

It was bewildering. I didn't know where to look first. "The reocrds mom, the records," Carrie insisted. "Remember last time?"

Last time, to my everlasting sorrow. I reached for the album "The Singing Nun," something I've wanted ever since I heard the song "Dominique," a fraction of a second too late. Someone beat me to it, and I moaned about it for days. This time, with Carrie's help, I found two exercise records and the soundtrack from "South Pacific." She also spotted some dance records, but they turned out to be too damaged; so we turned our attention to the books.

People were finding all kinds of things. "Agatha Christies over here," someone called, and I hurried over but got sidetracked by "Centennial" and "Roots." I lost out on the Christies> too late again. "Where are the psychology books?" "Anyone want books on travel? Gardening? Science? Art?" They were all there in a kind of orderly jumble, and it was surprising how many current books, both fiction and non-fiction, were available.

"How about these prices?" asked someone who'd already filled two cartons. "Fantastic."

Jeffrey dashed over beaming. "Look, a Spanish dictionary for children! Now I can learn Spanish!" He also selected two Curious George books and a Cub Scout manual.

"It's so hard toi see," he complained. "There's hundreds of kids around that table, and one lady bought about 25 books and put them into a big sack. Why do you think she wants kids' books?"

"She's probably a teacher or a librarian in a private school," a volunteer stopped to explain. "Lots of teachers come to these sales to buy books for their classrooms."

My husband found a stack of National Geographics and leaned happily up gainst a wall to browse through them, Carrie picked up a few Nancy Drew mysteries, and Linda bought "Ballet for Beginners" and a magazine with a feature story about Olga Korbut, her gymnastic heroine.

The room itself was quiet, really strangely quiet, as people milled around from table to table picking up books, reading a bit, putting them down, exchanging, trading.

"Oh, if you don't want that please could I have it?" I begged a man who had just picked up what looked like a very old copy of "Little Women." He considered, then said, "It's yours," handing it over. The copyright was 1922, a real find.

"There's some other old books on the table by the door," a woman told me. "I just found this old grammar textbook and an alphabet book in French." I hurried over, but the serious collectors had gotten there first.

A couple nearby was searching frantically. "We've got almost a complete encyclopedia," they said. "All we need is EL to GO, and we'll have a whole set. It's from 1958, but so what? The information is still right, and it will only cost about three dollars."

The sales are held, according to Donald Roha, chairman of finance for the library board and volunteer manager of the sales, "to clear the shelves of duplicates and donations. Ninety percent of the material we sell was donated to the library by private citizens." The sales are also "a way of getting books into the public's hands. Some children come here with a quarter or a half-dollar and, well, it's like watching a kid in a candy store, they don't know what to buy first. It's great to see them."

Of the money collected, 10 percent goes to the county general fund and 90 percent to the library committee, which uses it to buy equipment for the libraries - "something they really need, like a movie projector or a record player or display cases," said Roha.

"The sales are managed completely by volunteers. Some librarians come down and work, but they're volunteering their time. No one gets paid for doing this."

The sales are usually scheduled for the last Saturday of the month, "but in November and December it might be different because of the holidays," Roha said. "We usually put out about 10,000 items to sell and collect about $1,000 at each sale. People spend anywhere from a nickel to several dollars."

By 11 o'clock I was dizzy with looking at so many books, the bag on my arm was overflowing and getting heavier by the minute and the children were already outside lounging on the grass reading their collections. Carrie came back inside twice to buy more books. "I read fast," she explained. BOOKED FOR BUYING

The next library sales will be this Saturday at 11701 Georgia Avenue, Wheaton. The sales begin at 10 and last until about 2, but we think the early morning's the best time to go. Then you have the rest of the day for reading. Call the library, 949-4773, for future dates.