For years, I've thought about doing a column on the beetle-browed cretins who wait for you to to catch a fish, then steal your spot. Now I've been beaten to the punch by Lou Feierabend, who was molested but managed to exact sweet revenge.

Feierabend sent a note this week from Block Island, R.I., where he's been spending evenings surf-fishing for blues in a crowd of vacationing New Yorkers.

"I had one gripe about the other fisherfolks," wrote Feierabend, a consummate sporting gentleman, "but found a very effective antidote.

"If I am lucky enough to land a fish or two, others tend to move in, sometimes less than a rod's length from my position, and cast directly to 'my spot.' I asked one guy if he wanted to stand in my footprints. He made some remark stating the right of anyone to fish anywhere . . .

"I gave the fellow my place," wrote Feierabend. "He could cast but was totally ineffective otherwise. I went to the exact place he abandoned, caught two blues in quick succession. When the third and fourth were hooked, I handed the rod to my grandson, who beached both fish, all of this duly noticed by my victim.

"To me, that was the best catch of the evening."

Cheers for Lou, and here's hoping, but doubting, that the knucklehead he shamed learned something from it.

For the record, when two people fish side-by-side and one catches and the other doesn't, the chances are nine out of 10 that the difference is technique or equipment, not location.

There are so many variables in presentation of a lure that even two excellent anglers using similar gear would be hard-put to duplicate each other's offerings.

One might retrieve a lure slightly faster or less regularly; one might allow the lure to drop an extra foot or two before engaging the reel.

Just the way a lure is tied on can affect the way it travels; one might weigh a bit more; one might swim through the water differently.

And when two anglers using completely different equipment fish side-by-side, the presentations won't be even remotely alike.

Thus, if you're the one getting skunked, it's a far better idea, and certainly more mannerly, to stand back and try to figure out what the other fellow is doing differently than to wait for him to turn his back and steal his place. You might even learn something.

What to look for:

Type, color and size of lure: Feierabend said the mackerel and bluefish off Block Island were feeding on sand lances, and he found that by tying a bit of white deer hair onto his silver Hopkins or diamond jig lures he better duplicated the lance. Folks fishing the same lures, unadorned, were getting one-third the strikes he got. So tiny changes can make a big difference.

Depth: Judge how long the successful angler allows his lure to settle before he begins his retrieve. Fish might be feeding anywhere from the surface to the bottom, and the lure traveling at the wrong level is foraging barren territory.

Weight of line: Light line casts much farther than heavy line, sinks faster and is less likely to spook fish. Two anglers fishing identical tackle in the same way can have completely different results if one uses 12-pound test and the other has four-pound. But the fellow fishing the wrong-weight line can adjust, and must.

Speed and style of retrieve: The other night, I was fishing for striped bass with an expert in the Potomac. Mysteriously, I was doing the catching. The only discernible difference was that I was turning the reel handle as slowly as possible and his retrieve was medium speed.

Bluefish, by contrast, often want the lure retrieved so quickly you wonder how they catch up to it. Other species, notably white perch, strike best when lures are stopped in mid-retrieve. Largemouth bass often hit on the initial drop, before the reel even is engaged.

These are some variables that are plainly discernible by studying another angler at work. The sensitive fisherman studies and duplicates these and any others he can notice. Chances are, if he does right, he can fish with success in the same place he was getting skunked a few minutes earlier.

Of course, in one of 10 cases the successful fellow is casting right over an unseen slough on the bottom, onto a sunken wreck that holds bait or on top of a cold-water spring or some other natural phenomenon that attracts fish.

In that case, you can watch and copy all night and still not get a strike, and decorum calls for more direct measures.

"Hey, buddy," you might say, "did you see those three girls in the Jeep giving out cold beer?"

When he turns, you trip him, break his rod and move in.

He's been there long enough!