What has 154 bits of hollow tubing threaded onto two sets of 18 lengthwise nylon strings, all of it connected by 10 elastic cords and separated by five pairs of heavy nylon cross strings? A tennis racket, of course.

Never heard it? Then you didn't follow the controversy generated during the U.S. Open Tennis Tournament at Forest Hills last year over the spaghetti racket. That's the rug-beater of a star-beater that an unknown American prop named Mike Fishbach used to bury Stan Smith and Billy Martin in straight sets. It's the magic noodle that put side-spin, under-spin and convoluted tailspin on topspin shots while giving off a sound that makes the traditional "ping" of a well-strung racket absolete. The spaghetti racket just goes "clack," the same as when you break a wooden racket into many small pieces.

Though temporarily banned from all sanctioned tournament play, the spaghetti racket - a German creation - has now come onto the American market commertially, and it's available in most area tennis shops for about $100. Or, if you like the frame you've got but want some elbow-easing pasta in it, you can have a spaghetti kit wired into yours for about $40 insome stores. Its life expectancy is two to four times longer than conventional nylon or gut.

The spaghetti racket - officially, it's called the "double-strung" racket - may do for tennis hackers what the original Lacoste metal racket (known to most as the Wilson T2000) and, more recently, the outsized Prince racket have done: revolutionize the game. Which is why they banned it.

The new racket is loosely strung: 70 pounds for the five pairs of cross strings, but only 40 for the longitudinal strings - all top-grade nylon. The long strings on either side move in unison - thus the elastic holding them together - when the ball is truck. They look like the ribs of an accordian, getting a deeper, longer bite on the ball and imparting spins you've never seen before.

A flat stroke becomes a heavy topspin shot, which is what most of us need to keep the ball in court more often. Mis-hit shots sink in time to stay in play. First serves become an exercise in Phil Niekro knucklers - screwballs, sliders, fading curves. Another eason the frightened International Tennis Federation has imposed a ban.

The ban is a bother only if you're thinking of playing Wimbledon this year. Or if you have offspring moving up the ranks of the Mid-Atlantic Lawn Tennis Association (MALTA). And once the racket takes a hold on the popular imagination, as the prince did, the ban is probably doomed.

Europeans have been using double-strung rackets for several years. The contemporary model, marketed by Werner Fischer of Germany, was developed five years ago when Fischer, a horticulturist and very average club player, began tinkering with his racket to generate more topspin. His racket was a natural for European clay courts.

Australian Barry Philips-Moore, a middle-ranked player, began using the spaghetti strings on the pro tour last year without protest. One day Fishbach got a good look at philips-Moore's racket, ran home and stretched the thing from memory. After 18 hours of tedious labor, he, too, had a spaghetti racket. (The name comes from the 154 piece of spaghetti-like hollow tubing that make it possible for the long strings to move over the cross strings without undue friction.)

The real trouble started when Fishbach upset Smith and Martin last September. A number of other European pros joined the crowd and restrung their rackets for the fall circuit in Europe. The next upset was of Ilie Nastase, the nasty Romanian; he was thrashed at a Paris tournament by little-known Frenchman, Georges Goven, wielding pure weirdness. Nastase stomped and screamed and swore he would never again play against spaghetti.

At the next stop on the fall tour, Aix-en-Provence, no fewer than seven of 32 players were using double-strung rackets - including Ilie Nastase. And who should whip every body in sight with his handful of spaghetti, to gain the finals against Guillermo Vilas? Ilie Nastase. Then it was the turn of Vilas, the sometimes-petulant Argentine, to march off the court in protest after losing the first two sets in a best-of-five match.

The following week, at a kind of kangaroo court arranged in Barcelona, the ITF ruled the spaghetti racket an unnatural creation and banned its use.

Be all that as it may, the spaghetti racket is fun to play with. I've found that it improved my baseline play, gave all kinds of variety and reliability to my serve and saved many an overhit overhead. It also drove my opponents crazy.

But I also found it harder to thread the needle on critical passing shots, and it turned a weak volley into no volley at all.

They say it's great for tennis elbow; I wouldn't know, since it was my foot, my shoulder and my back that were killing me that week.

Recommendation: Just right for baseliners, clay-court artists and your medium-level club game.