"Come on down for a couple of days of deep-jigging big bluefish off Frying Pan Shoals."

That's the way the invitation read, and who could say no?

Big blues were almost a lost commodity in the Chesapeake Bay last summer. They were absent from the surf on Block Island, too, although we had come to almost expect a generous share of oversized specimens.

They never showed up off the beaches of the Carolina Outer Banks, where thousands of four-wheel-drive buggy operators congregated in November for the annual celebration of big bluefish week.

I must have seen thousands of freshly caught blues over the last six months, including all the ones I watched people cleaning at the docks. But I can remember only a couple that would have tipped the scales at more than eight pounds.

Then came this promise of bottomless pit of 15- and 20- pound fish. Who could say no?

We left Cape Fear at 5 a.m. on Friday, which I have to keep reminding myself was Dec. 8. It's hard to fathom because the southwest breezes carried damp, 70-degree temperatures even before dawn, and later in the day we glistened with sweat as the thermometer topped 80.

Frying Pan Shoals, it said on the chart, lay 45 miles southwest of the mouth of Cape Fear River and the neat and aged city of Wilmington. A long finger of shallow sand pokes out into the Atlantic there, extending almost to the Gulf Stream and the continental shelf.

At the tip of the shoal is Frying Pan Tower, a huge platform the size of a football field. It rests on steel pilings 200 feet above the surging ocean. A house covers the platform, living quarters for the workers who man the light that wards oceangoing vessels off the shoal.

Frying Pan has long appealed to fish, it seems. Commercial fishermen have used the tower as a guide to some of the best grounds for king mackerel and black bass.

But it's only been in recent years that big blues made a showing. "Five years ago," said our captain, Rick Carig, "if you brought a five-pound blue into the dock people wanted to take a picture of it."

All that has changed, we quickly confirmed. Craig slowed the engines as the boat passed under the tower's shadow and a huge pod of fish showed on the depth recorder.

"Good lordy, look at that," he said. "Get those jigs in the water, boys."

"You're going to hit them right now," he said. And we did.

Joel Arrington had one on first, and he grunted and sweated with the burden of the big fish on sporty light tackle. We were using four-ounce jigs tipped wiyh rubber worms. The line was 15-pound-test, lighter stuff than most folks use for freshwater bass.

It took him three or four minutes to land the fish, a 12-pounder. By that time we had drifted off the school. Craig turned us around and again found it.

This time we both hit fish, and battled them home in another five minutes. The longer we fished the better we got, and b efore long it was like taking cake from a baby.

Only Denny McCuiston, the mate, managed to keep up his interest. He'd never caught a blue on anything less than the commercial fisherman's 80-pound-test outfit. "Man," he exulted, "this is fun."

By noon the fun had filled our catch box with 10- to 15-pounders, and we were slipping little black sea bass into the chinks. It was getting to be too much of a good thing, so we called it quits.

Amazingly, McCuiston and Craig said the run has only begun. "There aren't enough blues out there to make it worth while to fish them commercially," Craig said. "In another month the price will go up in New many fish out there. That's when we'll get to work."

What brings the blues to this area all of a sudden? Stuart Wilk, who prepared a data book on blues for the National Marine Fisheries Service two years ago. thinks it's a result of overcrowding.

"Bluefish are so abundant they have spread out," he said."We've had them off Diamond Shoals in the winter. Now they're moving south." That theory is borne out by catch figures. Recreational and commercial catches of blues have almost quardrupled since 1960. And there's no end in sight.