HAROLD (not his real name) considered quitting only once.

At the time, he happened to be kneeling amidst a living room full of six-foot lengths of 2-by-2s bolted together to be somewhat rectangular. His jeans were covered with sawdust, and 3 bandage covered that portion of his left thumb assaulted earlier in the day by an errant hammer. Harold had just discovered that too much lateral pressure can snap a perfectly useful drill bit into two attractive but nevertheless useless stubs.

His wife, who had been on the telephone, chose this moment to enter the room and inform Harold that her parents would be arriving the next night from New Jersey to see their new apartment in Washington, and how were the shelves coming along?

Later, Harold would say that he felt much better after the primal scream (although he couldn't be sure what it did for the guy downstairs). And by the next afternoon, the seven-by-eight-foot shelving unit was complete: sanded, stained and anchored down by lots of books, a stereo and a fold-down dining table made of a hatch cover.

And you know what? It looked just like Real Furniture.

Harold's name was changed to protect his pride, but his story is true. He truly got the plans from a popular magazine. He honestly bought the wood and hardware at his local lumberyard, and he forthrightly built a good-looking shelf unit in one weekend's time, and for about $120. Which brings us to the point of all this nonfiction:

So can you.

In return for the relatively small financial and spiritual expensed involved in acquiring the necessary materials - tools, plans, lumber and a place to work - you will be rewarded with the satisfaction that comes with making something useful, inexpensive, attractive, and above all, YOURS.

WHAT TO BUILD?

The choice is yours. You can find plans for do-it-yourself furniture just about anywhere - in the magazines on the drugstore rank, in books you can buy at the lumberyard showroom or borrow from the library, or in the local newpaper. They vary from the one-hour, $5 plant box to the one-weekend, $100 bookcase to the three-week, $500 sleeping loft. It's a question of time, tastes, tools and money.

If you're just starting out and have neither many tools nor much time, the best place to start may be with the furniture plans found in one of the various home or apartment idea magazines. Apartment Life (where Harold found the plans for his masterpiece) usually offers two or three projects a month, and most of the ubiquitous "women's" magazines regularly either print plans for simple projects or allow you to send away for them, for a small fee.

Books for the potential amateur and professional furniture builder also abound. They vary widely in degree of difficulty and readability (see list below,) but most are invaluable as reference guides. MATERIALS

If you choose your first plans from a popular magazine, you may be led to believe that finding the wood and hardware you'll need will be easier than remote-control TV. Not necessarily. If you've ever been to a hardware store or lumberyard and felt the icy stare of a salesperson who has just heard you ask for a "doo-dad," a "whatchamacallit," or "some wood about this thick," you already know what true pain and peer rejection are all about. Next time, you'll want to be prepared.

The most basic classification of wood divides it into two types: hard and soft.In general, hardwood furniture is more difficult to work with but more durable than softwood. (It is also more expensive and harder to find). If you're just beginning, softwoods should prove more than adequate for most purposes.

Softwoods are available in a variety of conditions, or grades. The two grades you'll most often deal with as a furniture maker are Select and Common. Select is the best - it has good appearance and finishing qualities - and is divided into four subclassifications: from grade A (pratically free from defects) to D (can have any number of defects or blemishes, but still good for finishing).

Common grade lumber is considerably rougher and probably not suitable for finishes - but its cheaper price makes it practical for use as cleats, supports and various other furniture parts that are ultimately hidden from view.

No matter where you buy a 2-by-4 in Washington (or anywhere else), that board is actually going to measure 1 1/2-by-3 1/2. Ask for a 1-by-2 and you'll get a piece of lumber measuring three-quarters of an inch by 1 1/2 inches. This cute bit of confusion is known as the-Nominal Size-Actual Size Syndrome, and it is known to afflict one out of every three would-be handymen. All you need to remember is that the actual size of most woods you'll encounter is smaller than its nominal size - the size by which it is bought and sold. This due to the trimming that occurs between milling (carving boards out of trees) and selling. Actual size-nominal size tables can be found in just about every how-to book on the market, and most project plans will remind you of this reality.

The other type of lumber you're likely to deal with is plywood - usually sold in 4-by-8-foot sheets, constructed of thin slices of mostly softwoods glued together to make a stronger (and lighter) board than ordinary wood of the same thickness. The most common thicknesses range from a quarter to three-quarters of an inch, and plywood can be purchased with a wide variety of finishes and textures already applied to one or both sides.

If you don't have a circular saw, you will need to have most of your plywood and boards cut to size at the lumberyard. Harold once said discovering that lumberyards will actually cut lumber to size for customers was the single most important factor in his decision to become a master craftsman.

Most lumberyards charge extra for the cuts - anywhere from 50 cents a cut to $15 an hour, according to an informal check of Washington area dealers - but the time and toil you save will usually be worth the price.

Shopping for lumber is smart. It is also difficult to by by telephone, mostly because wood quality - even same-grade wood - can differ conspicuously. And the economy car owners among you may find a lumberyard in Gaithersbury that will sell you 2-by-2s for 40 cents less than the guy down the steet, but what-good is that if he charges $15 extra for deliveries under $50 more than 30 miles away? Most people seem to shop not for lumber but for lumberyards; once they've found a convenient, friendly place to buy high-quality wood, they stick with the place. TOOLS

Harold also once said the single most important factor that prevented him from entering the furniture-building business and thereby becoming world famous was the fact that he had no tools. He says the following will get you started:

A hammer, preferably with a forged steel head (rather than cast metal), for pounding and pulling our nails, and for damaging thumbs.

Two screw drivers - one regular with a blade about 1/4-inch wide, one Phillips head for appearance (Phillips head screws are against Harold's religion).

One adjustable 6-inch pliers, for holding things tightly and for bending or straightening.

One level, for making sure your furniture rises from the floor at the same angle you do.

One power drill, preferably 1/4-inch or better, mostly for boring holes but also for driving screws, sanding, polishing and keeping out or reach of children.

Measuring and marking tools, including: a ruler, preferably metal or at least metal-edged; pencils; a 10-foot or longer metal tape measure; and a combination square, for checking the squareness of boards, marking 60-degree angles for sawing or nailing, etc.

There are plenty of other tools you may need, and again it depends on what you have in mind for your nights and weekends. Most common tools among those otherwise regular people who have more than a passing interest in furniture are any number of saws (miter, crosscut, saber saw), clamps, chisels, planes, adjustable wrenches, power sanders and routers. If you only need to use a tool once, it might benefit you to rent it. BOOKS

One thing books will not do is build a coffee table for you: But if you've found a good how-to book, you will likely feel a lot more confident both behind the power drill and at the lumberyards; you will know the difference between a No. 10 wood screw and a 2d nail and that a rabbet joint is not a place where bunnies hang out.

A sampling:

Basic Carpentry for Apartments, by David Heim. (New York: St. Martin's Press, 1975), paperback. Illustrated, highly readable, humorous guide for the beginner, apartment-dweller or otherwise. Includes project plans.

The Furniture Maker's Handbook, by the editors of Family Handyman. (New York Scribers, 1977), hardbound. Color illustrated, technical run-through of everything you'll ever need to know about furniture building. Includes some rather involved plans.

How To Build Modern Furniture, by Mario Del Fabbro. (New York: McGraw-Hill, 1976), hardbound. Much like the Furniture Maker's Handbook, but a little easier to follow. Illustrated, and with plans for building Del Fabbro-designed projects.

Crate Craft, by (New York: Butterick Publishing, 1976), paperback. illustrated account of how to find scrap wood and then turn it into good, rustic, relatively easy-to-build furniture.

How To Make Furniture Without Tools, by Clement Meadmore. (New York: Pantheon, 1975.Illustrated instruction in building simple-looking stuff form pre-cut plywood and glue. See?