SHOW-BIZ types who have tried, and failed, to get a job with a circus freak show insist the surest method is to grow two additional heads. Wrong. The easiest way to get a job with a freak show is to paint an entire house of two-inch wooden moulding with a four-inch paint brush.

Try this and you will see that, afterward, your head will be locked in a position close to your knees, your arms will be forever curled up like prelzels and your face will be permanently contorted into the expression of a medieval gargoyle.

Freak show impresarios will be climbing all over each other trying to sign you on.

Most painters worth their latex can't be bothered with freak show impresarios, so they tackle two-inch moulding with a one or two-inch brush. Fitting the proper painting tool to the correct painting task is just one more way of maintaining dignity and obscurity.

Paint brushes, like rollers and painting pads, come in varying shapes, different qualities and wide-ranging prices. Brushes sell for as little as 20 cents, and for as much as $16 and more. The difference in prices is attributable, in part, to variations in size. But mostly it is due to the type of material used in the bristle and the amount of workmanship applied to the brush to make in perform well.

"Performing well," in brush-talk, means the ability of the brush to paint without leaving behind telltale brush marks. Quality is also measured by the amount of paint the brush will take from the can to the wall in one load, and the ease with which it applies the paint.

As a rule, says Jack Island, marketing manager of paint applicators for PPG Industries (maker also of Pitts-burgh Paints) in Pittsburgh, natural hog's hair bristles (preferably from China) are the best because they are the softest, most pliable and most clinging. They are also, as a rule, the most expensive.

Natural bristles, however, do not take kindly to the water in latex paints, which makes them swell up. So the industry has come out with synthetic bristles. Polyester and nylon are the most common.

Nylon brushes are the least expensive of the lot ( $2-$4.50 at Sears) because they are stiff and coarse. They can, says Island, leave behind little "valleys" in the paint film that look odd and collect dirt. So many companies have ventured into a middle ground with polyester-nylon brushes ($2.50-$8.50 at Sears) that combine, Island said, the softness of polyester with the durability of nylon.

You can spend all day picking out a good paint brush. Take a moment to examine the ends of the bristles. There are tapered bristles (good) that end in a point -- and there are non-tapered bristles (bad) that look as if they ran head-on into a brick wall.

Natural bristles are naturally "flagged," meaning they have those otherwise despicable split ends. Good synthetic bristles have been mechanically flagged for the same effect.

And the best brushes have that "layered" look. The bristles are of varying length to achieve an optimum "80 percent top," as Island calls it. This, the flagging and the tapering are all designed to make the brush paint more smoothly and easily, and carry more paint. You can test softness by drawing different brushes lightly across the back of your wrist.

If you have a few hours to poke around, you can also squeeze the bristles together and look inside. The size of the "fish mouth," or empty space in the middle, tells you how much bristle the manufacturer puts into his brush. The more bristle the better.

The National Paint and Coatings Association places brush types into three categories: wall, enamel and sash. Wall brushes are most commonly found in four-inch widths. They are meant for painting broad surfaces on either walls, ceilings or floors. Enamel brushes are usually one to three inches wide. Use these for painting woodwork, such as baseboards and trim around doors. Sash brushes, easily confused with cousin enamel, are distinguishable by their longer, narrower handles. They are best for painting window sashes and "cutting in" around tight spots. Some have bristles cut diagonally across to leave a handy point on one side.

If you choose the right brush for your painting job, you can avoid calls from freak show impresarios and also bending your brush into funny shapes.

After brushes, choosing a paint roller is a relatively simple matter. But this is no reason for haste.

In stores you will find roller covers sold under such names as "economy," "better quality," and "one coat." At Sears these are priced as 50 cents, $1.79 and $2.29. Cheaper covers are less consistent in fiber density, which can cause "matting," or a blotchy, uneven coating. Their inner cores are less well constructed and can eventually dissolve away.

Covers also are labeled according to "nap" (the length of the fiber), usually short, medium and long. The general rule to follow is long naps for rough surfaces (brick or cement) and short naps for smooth (plaster, wood and wallboard). For very smooth, glossy finishes with oil-based paints, the NCPA recommends a mohair cover with the shortest possible nap, althogh these types, by and large, do not hold much paint.

Like brushes, rollers come in different sizes: usually seven to nine inches for large areas; smaller for corners and hard-to-get-at places. There are even V-shaped rollers for painting in corners and sponge rollers for acoustical tiles.

Originally intended for painting exterior shingles and siding and for staining, painting pads (square blotter-like applicators of fiber on a foam backing) are becoming more popular for general painting jobs. Island says pads now command about 15 percent of the total commercial market. They don't spatter, and leave a smoother finish than rollers, says Island, and cost about $10 at Hechinger for a kit including a large mohair pad, a small trim pad and a plastic tray.

The pads have struck a chord, apparently, in our throw-away society. Once used, they can be discarded and replaced.

Quality brushes and rollers, on the other hand, require proper maintenance. The better ones reward their careful owners by lasting a lifetime. But cleaning up must begin immediately, before the paint begins to dry. Latex paints should wash out in warm, soapy water. Tools used with oils need a bath in a mineral spirit solvent.

When the roller cover rinses clean, it can be stored in aluminum foil, but should not be mistaken for Polish sausage in the freezer. A cleaned brush should be dried with a rag, then combed out with a metal paint comb ( $2- $3). Wrap each individually in plastic, or in the original container.