A FRIEND RECENTLY moved into a house with a real honest-to-goodness Dining Room just in time for Thanksgiving. She was so excited she went off the deep end and invited 20 of her closest relatives for a Thanksgiving feast. But then she'd lived three years in deepest Rowburbia, where the builder expected everyone to eat on TV tray tables.

Not only did they buy a house, they also bought the work of a painter, an electrician and several worthwhile but inexperienced moving men. Obviously they don't have the money now to go out and buy the Williamsburg dining table they'd like. There really isn't any reason why they have to. A dining table is one of the easiest of all furniture pieces to fake. And there's time to do it before Thanksgiving. Such made-up tables are also great boons to people living in one-room apartments or other temporary space because they don't require a major investment.

John Wiebenson is an architect who hates spending money for such luxuries as a dining table, but his wife Abigail loves to feed people. So together in their Dupont Circle townhouse they have put together all sorts of cost-free tables. For years they've owned that cliche of the make-do school of architects, the table made out of the telephone-wire spool found in the alley. (The cliche of architects who have made it is the Mies Van der Rohe/Lilly Reich glass coffee table). Recently the Wiebensons found just the top of such a spool, so they added four 2-by-4-lumber legs, made from old wood ripped out of the house in remodeling, and made an outdoor table from it.

Pepco will give away such spools free - you don't have to steal them or find them in the alley - at 3400 Benning Rd. NE between 7:30 a.m. and 3:30 p.m. You might want to call first, 872-3314, to see if they have one when you want it. Wiebenson also has the useful between meals as a desk or drawing board. The table, with rough planks replacing the door, goes back as far as people have feasted.Remember the Peter Bruegel painting of the feast. And George Washington at Mt. Vernon used them for his banquets in his great room; the sawhorses and planks were put in for feasting and removed for dancing. Think how many people you could seat at a 4-by-8-foot sheet of plywood! Be sure you get it thick enough so it won't collapse in the middle.

Another architect, Milton Shinberg, inherited a variation (you might call it a modern adaptation) from an older Beaux Arts architect, the late Cyrus Wood Thomas. The Thomas table is a door with metal pipe screwed into metal phlanges on the bottom. The result can be more lean-proof than the door balanced on saw horses. And the only tool you need is screwdriver.

The Door Store started out with, as its name suggests, this simple concept. Currently, it has embellished the idea to add stainless steel sawhorses and marble or glass tops, at, of course, several hundred dollars more. But the basic material still works very well. The average door will seat six comfortably, eight if they're close friends.

You could, of course, drape the whole thing in mother's best Hong Kong hand-embroidered cloth. That's the posh way to go. But there are alternatives. Sheets - especially the fancy ones now on the market - make superior tablecloths, especially for the long table. Hem the sides, if you're handy with a needle and have a stern conscience. The rest of us rise above it on the grounds that no one will look down there . Sheets can be made into circular cloths by the nimble. The French Embassy, a few years back, made round cloths out of Christian Dior sheets.

The door and the sawhorses could also be sanded and finished with stain to match your woodwork or your eyes. In the right sort of house, both door and saw horses could be painted bright colors. With enough masking tape, a steady hand and enough time, you could do a brilliant painting on the top of the door - perhaps a circle of color for each place setting. Be sure the paint is dry before you have people to dinner, unless you want to have friends with multi-colored elbows.

The best of all doors are the ones that don't cost anything - the doors you save from your remodelings. You have to take off the hardware, of course, and fill the holes with wood putty. The paneled doors don't work as well, because of a regretable tendency for plates to fall into the panels. You can bridge over a paneled door with a thin sheet of plywood. Though it seems a waste because paneled doors make such good looking paneling or, cut down make cabinet doors.

Once I covered a door with those 12-by-12-inch mirror tiles you can buy everywhere. I used the two-sided stickem whatchits that come with the mirrors in the package. Then my husband painted the edge black. We used an off-size aluminium frame as the base. It looked so good, a magazine threatened to come out and photograph it. Everyone marveled for some months, until a child overturned vinegar on the top - and several edges of mirror turned black if we'd had the courage, we could have pried up the tiles and replaced them with new ones!

You could also use wallpaper, fabric, old New Yorker covers, playing cards, posters, whatever. Glue it all down with wallpaper paste and put several layers of clear polyurethene lacquer over it.

Jacqueline Kennedy Onassis, when she was Mrs. John F. Kennedy and the first lady, used in the Blue Room what Clement Conger, the curator of the White House has been pleased to call " a contraption." A pasteboard cylinder with a round plywood top was covered to the ground of course, with a fancy cover.

Those round packing cylinders would work like a charm as such a base. It doesn't have to be round. I once used a good square pastboard box. You might want to ballast it with something like a bag of sand. (Be sure the bag is intact - nothing is harder to clean up from the living room than said. If you are truly useful, you can make a pedestral from plywood (it warps less). In a tight space, make it so that land horizontally the base serves as a cocktail table base, turned vertically, it's dining height.

Hechinger's sells rounds of plywood or pressed wood up to 48 inches, ideal for tops. Woodward & Lothrop and The Hecht Co. Sell folding rounds which can rest on card tables to enlarge them to seat six. A man with a saw, a steady hand and the ability to draw a circle could make his own out of plywood. You'll need a good heavy thickness, at least 3/4 inch.

Jack's Roofing Co. on River Road sells slate rounds for under $30. They are far too heavy to be supported on your average moving van pasteboard whose top was lost in the move. We use two of them outside on two old restaurant pedestrals with ruined tops we bought at Goodwill Industries.Twice now we have found round marble tops at plywood prices in the want ads. Hefting them home makes them seem like less of a bargain.

The fanciest dining table we ever owned was an octagon, made of an exotic wood called zaricote which grew in the backwoods of Beline, Central America.

Having it made was not the easiest thing we ever did. But in Beline, there wasn't much to occupy your time, after the morning coffee parties, the noon lunches, the afternoon cocktail parties and the colonial service's dinner parties - and of course, the afternoon nap and the three baths.

We thought an octagon would be just the berries. Why I forget. Unless it was because back them we had eight forks, knives and so on. At least with an octagon, you can easily check to be sure you haven't missed setting a place.

We chose zaricote because it is the most beautiful wood I have ever seen, with zebra stripes of dark sky against light dawn clouds. It is as heavy as iron wood. We were told zaricote, too, sinks rather than floats. Considering the number of times Belize is under water because of hurricanes, this ability to sink is not altogether an advantage.

The local carpenter, it would be an exaggeration to call him a cabinetmaker, was a bit uncertain about just exactly what an octagon was. And when we told him, he was certain he couldn't draw one. So my husband made a paper pattern.

And that's where the carpenter, anxious to please and inspired to make a masterpiece, went astray. He cut the zaricote into a billion bits, forming triangular sections. And then glued them onto a sturdy mahogany back - mahogany in Belize is the cheap wood, sort of the yellow pine of the country.

He did warn us that we should hastily put a lacquer underneath and on top to seal the wood. But we couldn't find the right sort of lacquer in Belize (not surprising since there were weeks when you couldn't buy needles or even bananas). So we put it off. And then came the hurricane, soaking everything in the house very thoroughly. We thought we'd better give the table a good while to dry out.

Several months later, we moved on to Vienna, away from the tropical dimes and back to central heating and dry European air.I suspected all was not well when all night long, we could hear snap, crackle, pop, as though there were bowls of Rice Krispies in the living room.

We want to set the table for our first fancy dinner for my husband's senior officer. I put the plate on one side of the table and it slid to the other side, but not straight, sort of a curve. When I crouched down and looked at it at an angle. I realized for the first time what a parabolic shape is. The mahogany had warped one way, the zaricote another.

We kept it around for some time as a sort of accidental sculpture, listening at night to the pieces popping off.

That's when we bought the iron cafe tables - with lion heads for feet. Back them, the Viennese restaurants were all getting rid of those tacky old marble-topped tables with the iron bases and putting in really classy plastic laminate tops on tipsy steel bases.

We used the tables for years with a hunk of used, unpolished marble we'd bought in a Viennese equivalent of an old bottles and metal shop. Back in the United States, when we had saved our pennies, we bought the bases much bigger circles or marble, all new and polished. Nobody told us we had to put a piece of thick plywood underneath to support the marble. So one of our then small daughters leaned on the corner and the corner fell off.

Under duress, the marble company rodded the corner and epoxyed it back together. It hasn't fallen off since.But we always try to seat people with heavy boots at the corner.

All these contraptions work well enough and most are cheap enough so you can have several to accomodate more people than you'd care to cook for at Thanksgiving and Christmas. But there is one word of warning that applies to all tops not fastened down: If somebody on one side leans their elbows on the table, be sure everybody on the other sides leans too.

Other ideas for more complicated but still quick, cheap and easy tables can be found in: "Instant Furniture" by Peter S. Stamberg, Van Nostrand Rembold: "Fast Furniture," by Jon Zegel Running Press and "How to Make Furniture without Tools," by Clement Meadmore.