You can breathe new life into old, tired tennis balls, keep sweaty palms from slipping up mid-backhand, soothe tennis elbow and stretch an extra set from patchwork sneakers the big toe is peeking through. Such are the claims made by the season's latest tennis gizmos.

No one says gadgets are any substitute for dependable equipment (and lots of practice), but gadgets can provide a few laughs while you tweak the strings back into shape.

A quick survey of the latest wizardy on pro-shop shelves revealed the gadget industry's dedication to rejuvenating squishy tennis balls.

At $40, something called "Tennis-Pump" was definitely the Gucci of ball-restorers. Only thing is you'd have to pump up a lot of balls to break even.

It seems a bizarre little machine, with a pressure gauge on the side and a cone-shaped opening for the ball. Plop, the ball goes into the catbird seat, where it is catheterized, shot full of air (keep your eye on the gauge), sealed with goo at the proper pressure and , voila, an (almost) brand-new ball. Kind of like fixing a flat tire.

No one would vouch for the restored ball's longevity, but, it was lightly suggested, had Ponce de Leon been a player, his tennis balls would have applauded technology's answer to the fountain of youth. Of course, he could have simply purchased a new can.

Another ball-saver on the shelf was slashed from $6.95 to 25 cents at Arthur Ashe & Friends downtown.

Behind every bargain, of course, there is a reason, and the reason for this bargain, laughed salesman Dave Flannagan, was that "It was a complete failure. When you injected a ball with the chemical, it expanded but the hole didn't close. So the stuff dribbled out. We had something else called 'The Shot,' but we had to send that back to the factory, too."

There are a number of goodies on the market that promise to prevent tennis balls from running out of air in the first place. "Tennis Ball Saver" ($9.95). a pressurized, screw-top plastic container, promises balls a home away from home by maintaining the pressure of the original can. "Nu-Ball" ($7.95), a pump with pressure gauge, fits atop the original can and does the same thing.

Re-Fuzzer ($3) does just what it says it does. It re-fuzzes fuzzless balls. Just rub one around in the prickly mit of this gizmo - it looks like a mini-juicer with plastic thorns - and fuzz on the ball stands up as proud as Orphan Annie's curls.

For tennis buffs with no pockets, there is a ball clip ("The Third Hand," $1) that fastens onto shorts and holds one, count it, one ball. For players who ride bikes there is a nifty clip-on device that fastens racquets to bicycles. So, if you don't get a court, take a pedal.

"Shoe-Goo" ($3), a liquid rubber cement that dries overnight, can plug the toe-hole in your tennis shoe. But "Nu-Toe" ($2), a rubber bumper that fits rights over the tip of the sneaker, means a brand-new toe.

There's a lace-it-yourself kit called "Racket Guard" ($2), to protect the racket from its master's angry chops and smashes to the court. And for master's tennis elbow," there are innumerable restoratives, including "Don Joy's Warm-Up Sleeve" elbow and keeps it secure and warm.

You can stop your gut from slipping and fraying with "String-a-Lings," tiny plastic clothespin-like devices that keep the strings apart ($3).

As for sorry grips, well, "Grip Tape," may be the answer. The latex tape, available in green, red, blue or brown, wraps around a leather grip. Just the thing to keep sweaty palms in place, it was agreed.

There was some dispute, though, over exactly how balls do lose their bounce.

Flannagan, formerly of the Frostberg State College varsity tennis team, has experienced such dilemma firsthand. He suggested that balls begin to die the moment they leave the womb. "If you open a brand-new can of balls and don't touch them, they'll get flat just sitting out," he said.

Serious players, no doubt, will scoff at such manufactured magic. But who dares argue with the resurrection of a dead ball that's lost its bounce? Indeed, proof of a miracle.