If you get a kick out of fishing, no doubt at some time in your life you have been struck by the compulsion to try your hand at fly fishing for trout.

It's the most demanding angling there is, and most fly fishermen will tell you it's the most satisfying.

For once do yourself a favor. Say thanks, but no thanks. If you say yes, the biggest fish you'll land is yourself.

"Trout fishing is like a drug addiction," says Rocky Stump. "Guys work all week in the office and then on Saturday they have to get to the stream. They have to fish. And they have to keep fishing until they get their fix. Then they can go back to work."

Stump is hooked, so he knows. He finally gave up all pretense of real work and devoted himself full time to the pursuit of trout. He's the Washington area's only professional trout guide, on the days when he's not squiring customers around from stream to stream he's working at Angler's Art in Georgetown, tying flies or drumming up trout trade.

Stump is also an amateur psychologist. In watching his clients all summer he's come to some conclusions about what makes them tick.

"Trout fishing is an extroverting sport," he says. "It's completely consuming. You can't be thinking about your job or your family. There's only one thing on your mind - that fish down there."

The fly fisherman wants to put himself out of the picture. He must walk softly, hiding behind the brush and working his way upstream, scanning the clear, shallow waters for feeding trout.

When he makes his find the mental wheels begin to click. What is this fish eating? How should the fly be presented? How can I get to him without spooking him?

If the fly fisherman has to crawl through mud on his belly to cast to a trout, he'll do it. If has to hang by his toes from a willow branch, he'll give that a try. He leaves all affectations of dignity behind. The only thing that counts is the fish.

That may explain why many of Stump's clients are high-visibility professionals - doctors, lawyers and businessmen whose jobs put them in the public eye. For a change it's their job to be invisible; all eyes are on something else.

Most of Stump's parties are bonafide trout anglers already, but need his services to bypass the time-consuming chores of scouting streams and doping out the feeding habits of the fish. So his job is a tough one. He's got to know when to be there and when not to.

"The last thing a trout fisherman wants is somebody hanging over his shoulder when he's working a fish. I try to play it by ear; if a guy needs help, I'll help, but if he doesn't I get out of the way."

And while Stump does his best to weed out the novices, or at least prepare them with a few casting lessons on the C&O Canal before they hit the big streams, there's always a lemon or two that squeaks through.

The only time a client of his was skunked, Stump says, was an old-timer who assured him he could cast."He got at least 10 fish on his line, but he never set the hook. He didn't know how."

Other than that just about all the guided ones have been trout junkies already. Many are reacquiring the habit after years of abstinence.

What their trip with Stump does is draw them a map - where to go and how to act when they get there. His fields of plenty are the Pennsylvania limestone streams, four fish-for-fun areas that provide consistently good angling all year around.

The streams - Falling Springs, Big Springs, Yellow Breeches and the Letort - are to fly fishermen what twinkies are to the junk food freak, what bloomies is to the fashion fiend.

If you're already hooked and don't know where to turn, dig up Rocky Stump at Anglers Art and he'll give you your fix for about $60. It'll get you by for a week or so.

If you're not and somebody's pushing you, think about how nice it is to sleep on the weekends, how much you love your wife and kids. Tom Paxton put it this way in "Can't Help but Wonder Where I'm Bound": "Nail your shoes to the kitchen floor, lace 'em up and bar the door, thank your stars for the roof thats over you."