IT'S HARD TO TELL. There are no outward signs. No monofilament line stuck between the teeth, no fish-hook scars on the fingers, no hand locked in casting position. Not even a tweed hat decorated with "elk hair" flies, silver spoons, "Fat Getzits" and black jig, or a vest with a thousand pockets, or hip boots folded down at the knees.

If you didn't know differently, Jerry Zabriskie would look like any other fisherman - assuming first that he fished - with more stories to tell than fish tofry; with more reasons why fish don't bite, than bites.But, if there were such a thing as a perfect "10" in fishing, Zabriskie would be it. Those who've fished with him say he's the very best.

Gean Snow, an angler of some note himself, quick to give credit where Zabriskie modestly prefers not to, said he believes there are no 10s in fishing "nowhere in the world. But Jerry there's a nine . . . and I only know two, no, maybe three, and I'm not one of 'em, not even close."

It's difficult to define great fishermen. On any given day, placed in the right spot, and given the right lure, anyone can be great.

In Zabriskie's case, it's said he can catch fish where there are no fish. One companion joked that fish walk across land to get to Zabriskie's lures. Any day, in any water, at any time, he can catch fish, sometimes to the point of being obnoxious. That's a great fisherman.

Like the time, remembered Snow, when a group of skilled anglers went fishing for silver salmon in Alaska. Fishing the same river, using the same fly, during the same hours, within feet of one another, Zabriskie caught more salmon in a day than the entire rest of the party totaled in two.

What makes Zabriskie so good, they say, is he works hard at it, is willing to try new techniques, and fishes with a competitiveness that won't take no from any fish.

When he was learning to fish the Provo River, for example, and not doing well, he sat on the bank one day and watched an older fisherman that was. Taking what he'd learned, and mixing it with a new rigging he'd worked up, he developed a technique known as the Provo River "Bottom Bounce" . . . split shot on the end of the line with two droppers, or branches tied up the line for the flies.

"It was deadly," Zabriskie said with a broad smile. "I caught a lot of big fish. A lot of big fish." Now it's a common technique of good fishermen on the Provo.

True to his competitiveness, when he mastered the Provo, he pulled up caddis flies and sinking line and moved to another water.

"That's the way it's always been. Once I master a water I move. Most of the time I never go back," he admitted. "I like the challenge. When I try something new, I work hard to master it."

Not everyone, however, appreciated his successes. When he went to work on Flaming Gorge after the big Macks, there were those that would sooner watch Zabriskie sink than his line.

"After dragging (trolling) all that steel (line) around one day, I was ready to quit. I decided to try something else. I couldn't see why jigging wouldn't work. The first day I tried it I caught five fish in two hours. Two were over 20 pounds."

Soon he was catching fish, big fish, with what many of the Gorge regulars, most of them trollers, found as annoying regularity. Now, even some of the guides are jigging rather than trolling.

There are, of course, other things to being a master. This, many have said, is what pushes Zabriskie over a "9." The master is also a teacher. To anyone that asks, and even a lot that don't, Zabriskie will spill out a chapter or two on style and technique, and usually follow it up with a sample or two of the right tackle.

He is now engaged in another competitive fight. This one's with his heart. Three years ago doctors gave him a year, at most, and suggested a transplant. Not one to let fishing line get old, dry and crack, he instead went fishing . . . and has been fishing as much as possible every since.

The result is that he's alive, feeling better than he has in years, and has the doctors ready to take rod and reel in hand for a little therapy. His heart condition, doctors have told him with grateful surprise, has stabilized.

Zabriskie flatly attributes his better health to fishing. "Nothing else it could be," he said.

And with that he loaded rods, reels and tackle boxes and headed for Lake Powell, his latest conquest, to do a little self-therapy on the bass there.