Have you ever received a second-hand gift? Have you ever given something not only old, but also worn?

For most people, unthinkable.

Mentioning Christmas-shopping in July is of course as incongruous as adding peas to ice cream. But to secondhand shoppers, it's already seven months later than one ought to begin. You need to spend in time and thought what you are going to save in money.

And -- if you can get out of your hammock -- summer's a fine time to prowl the flea markets and moving sales.

Last Christmas when our resources were temporarily cut in half and when even Santa was counting the cost, buying secondhand gifts became our only alternatie. Last year we shopped secondhand from necessity; this year we will be choice.

Our family's apprenticeship in secondhand buying began in England, where in the late '60s we spent a pound a week at a damp and drafty Yorkshire auction buying furniture for our equally damp and drafty Victorian flat. We grumbled all the way home about the weight of the wood. Later the sale of the mahogany wardrobe, one which cost more to deliver than to buy, financed our tickets to the United States.

We have purchased secondhand gifts on occasions when doing so was the only way of finding what we wanted: From a garage sale came two dozen issues of Gourmet magazine for a friend's collection; from a flea market, a willow picnic basket which we filled with china and gave as a wedding present; and from the bazaar came the patchwork quilt which covers the bed of our godchild.

A friend who isn't civilized unless she drinks two cups of tea before rising received a $2 oak breakfast tray and for the collection of another friend we found a sweet grass Indian basket for $20.

Buying secondhand for Christmas, we discovered, meant being able to ignore -- and avoid helping pay for -- the advertisements that flood the consumer in December. It meant shopping without the accompaniment of either music or crowds and it meant discovering that the cards of December were not followed by the bills of January: Charge cards are of no use in secondhand shopping.

By having to invest more than dollars in the selection of the gifts, we found we enjoyed orselves more and may have moved, quite inadvertently, closer to the intended spirit of Christmas giving.

Whether you choose to give secondhand Christmas gifts by choice, or by necessity, there are a few things to observe to avoid delivering the essence of an insult. (Unless cutting your list of friends in half is a desirable economic measure in itself.)

Never imply that your purchase was a financial necessity. Talk about the serendipity of secondhand shopping or the virtues of creative recycling; the gas saved by shopping on foot through the neighborhood garage sales, or the possibility of the gift being, or becoming, an instant antique. Describe the necessity you felt to get off the roller coaster of conventional Christmas shopping.

But don't attempt to pass off the gift as new. Admitting where you got it and what you paid for it becomes half the fun, for you especially. In fact, you'll quickly discover that claiming how little was paid becomes almost as impressive as knowing how much.

Secondhand shopping is not, of course, for those who shop by phone, or for those who must carry home bags announcing where they have spent their money. But it's a splendid way of getting to know a community. The conversations, the turnout, the merchandise, the prices and the people will tell you as much about a neighborhood as any other source.

Is there someone for whom a secondhand gift would never do? If the gift is an obvious reflection of the person's interest, if it reflects a day, or a laugh, or a conversation you had together, and if you still receive a cold or incomprehending stare, you have not just lost a friend, but gained a litmus-like test of friends worth having.

You might, however, give some warning that you intend to step off the Christmas roller coaster. The year my sister got off hers, she gave envelopes announcing that she had sent a gift to a cause she endorsed in the name of each member of the family. While we opened the envelopes, she sat and unwrapped packages from us to her, an effect she hadn't quite intended.

In our search last year for Christmas gifts, we found that the list we took shopping contained not what we were looking for, but whom. Would we ever have thought of searching for a farm mailbox complete with red flag for the brother-in-law whose heart is really in the country? Nor would we have expected to find it in September at a church bazaar.

A 50-cent phonograph without needle became a superb three-speed racing track for Lego trucks; a red felt wrap-around skirt, our Christmas tree skirt.

We picked up books throughout the year, most of them in new condition. For $5 we got 50 used children's paperbacks which went to cousins and the children's friends, all except the ones we claimed first for ourselves.

"Revelations," by Bethesda author Phyllis Naylor, a book which has been sold to Hollywood, went to a Canadian National Film board researcher. The hardback purchase set us back $1.

At Second Story Books we found the "Upstairs, Downstairs" cookbook for our English granny who once set the table upstairs herself.

"Upstairs at the White House" and Jackie Kennedy's guide to the same place also went to England, both bought for a quarter at the Chevy Chase Methodist bazaar. The same place provided the World War II volunteer nursing pin for our 5-year-old who has already decided on her career.

The school fairs, not surprisingly, were the source of the best children's gifts: a British made three-wheeler from the Beauvoir sale ($10), a dollhouse filled with 20 pieces of wooden furniture ($1.50) from the National Presbyterian School, and an $8 tumbling mat from Lafayette School.

Both girls got muffs, one in velvet and one in rabbit's fur, found at the thrift ships of two D.C. churches: St. Albans and All Saints Episcopal. tTheir plaid taffeta dresses together cost $15 at Kid's Stuff, a jewel of a consignment shop for dollar-conscious parents.

Under the tree sat an IBM electric typewriter for the parents, a purchase which cost $40 at a Cleveland Park garage sale and $20 to repair.

What we couldn't find secondhand we made at home, and we started early during our summer vacation. The leather lacing kit for a $1 made eight bookmarks to give to the ballet, the swim and the school teachers. Plaster of paris molds of Father Christmas were made for each of the cousins over 5 to paint; those under 5 got photo albums filled with art gallery postcards chosen leisurely by our two children.

Potato-printed supermarket bags -- an ideal, outdoor summer project for children -- have now begun to cover packages for the clan. We also collect newsprint for wrapping, geared to individual interests: copies of Art Buchwald's and Ellen Goodman's columns, photographs of Washington, sport-page headlines, recipe collections, and the front page containing the dateline of the recipient's birthday.

We not only intend to give secondhand gifts again this year, we intend to ask for them. Our small children would think it a treat, indeed, if they found a trunk full of discarded jewelry, makeup containers, dresses, scarves, shoes, hats and purses.

They would enjoy a fabric box: lenths of material or ribbons in various textures and colors to cover dolls (or themselves), or to make into belts, scarves, shawls, skirts. A work box containing a hammer and nails in various sizes and containers, padlocks with key and combination locks, and a flashlight would be welcome. And they would love broken things to tinker with: a record player, golf ball, alarm clock, radio, watch or camera.

There will, of course, always be some new things under the tree. Last year when we showed her the second hand on her store-bought watch, our daughter said, "But I thought this was new."