IF YOU WANT to catch the early crab," the man on the telephone said, "drive on down to Wye Landing and see Charlie Schnaitman and do exactly what he says." Wye Landing does not appear on the official Maryland map, so it was necessary to call the man at the Department of Natural Resources again.

"Just cross the Bay Bridge and follow the signs to the Why Oak," he said. "About a half-mile past the tree you'll come to Wye Landing Lane. Can't miss it."

Didn't. And Charlie Schnaitman was happy to put two suburbanites in a rowboat with bait and a bag of ice for less than $9.

"Oh yes, there are crabs out here," he said. "Good size too, for as early as it is. Hand-lining, a man might catch a dozen or a dozen and a half keepers in the day."

Schnaitman is a waterman and his son follows the water, but he seems to have overcome the Bay man's natural prejudice against "durn chicken-neckers," the amateurs who come to the Chesapeake and its tributaries to catch the crabs by which most of the watermen earn most of their hard living.

In fact he recommends chicken necks as bait. "I've got salteel, but chicken necks work as well and you get more for the same money," he said. Real crabbers use short sections of eel because they stand up better to being soaked in salt water and attacked by the sharp and powerful claws of the blue crab.

"Get out there in about six to 10 feet of water, about as far offshore as those fellas across the river are," Schnaitman said. "If it was me, I'd try that little point yonder. The tide will slack about 10:30 and things may go slow for a while, but then it'll pick up again.

The Wye is wide and beautiful, especially in the cool of a June morning. A half-hour in a boat was all it took to make a newcomer understand why local residents fought so hard to stop the development of Wye Island. The next half-hour was stop the development of Why Island. The next half-hour was spent wondering why the Wye's famous crabs - said to grow bigger faster than anywhere else on the upper Bay - were ignoring the chicken necks.

The novices finally discovered that the bait, tied on 12-foot lengths of string, was streaming in the current instead of sinking to the bottom. The blue crab can swim very well but'd druther not, preferring to scavenge along the bottom or bury itself in the mud and lie in ambush.

Weighted with one-ounce sinkers, the chicken necks began to do their stuff, although it took a while to learn how to tell a crab was working on one, because the current drag kept the bait lines in continuous and erratic motion.

The telltale was when a line assumed an angle different from the one beside it; the feasting crab apparently was trying to drag his find off to some private place. Occasionally a crab would be content to eat the bait where it lay, in which case the tipoff would be tiny oil slick blossoming on the surface, as the rending pincers squeezed out globs of liquid fat.

But getting crabs "on" was one thing, getting them into the boat another. If you snatch at the line the crab may let go. If you bring it in too gently the crab may let go. If the line fouls another while it's being drawn in, he may let go. If, as the bait nears the surface with the crab attached, you delay too long before netting him, he may let go. If you attempt to slip the dip net gently under him as though he were a trout, he will let go. If you do everything just right, he may let go anyway.

The suburbanites missed two crabs for every one they boated, but by the slacking of the tide they had a dozen in the cooler. Each was measured with a plastic device distributed by the state, and every one was a keeper: five inches or more from point to point, including one that had points curved almost into hooks and another that had lost at least a full inch off one end of its top shell.

One of the beasts was a seven-incher weighing perhaps half a pound, a "jumbo" such as seldom is offered in restaurants these days. He snipped through a strand of the heavy nylon net, demonstrating why real crabbers use chickenwire scoops. All of the crabs were "fat," fully filled out and approaching the time when they would once more have to cast off their shells to make room for more growth.

"You'll probably be throwing a lot of them back," the information officer of the Department of Natural Resources had said. "It will take another full moon or so, another shedding, before the majority of them get to legal size." The Wye was living up to its reputation for harboring the early keeper crab.

At slack tide the action died away as Schnaitman had predicted, but a great blue heron glided in to entertain during intermission. He wheeled and flapped as though showing off, and finally landed to stalk the shallows 25 yards away.Overhead, songbirds chased a crow that was chasing a turkey vulture that was pretending to be a hawk.

Impressive as the scene was, the suburbanites wanted the crabs to come back. A passion for the white, sweet meat of blue crabs cannot be resisted, and their appetites had been whetted to the ragged edge over the long winter by William Warner's Beautiful Swimmers, a Pulitzer Prize-winning celebration of the cantakerous creature whose scientific name means beautiful and tasty swimmer. The alternative to catching your own is paying up to $1.50 apiece for them; considering the yield of meat per crab, that amounts almost to caviar prices for a delicacy a true trencherman will gobble for hours on end.

When the tide turned, two chicken necks were seized simultaneously by a pair of big "sooks," mature female crabs that apparently had been caught by last fall's early freeze before they could make it to the wintering grounds near the Virginia Capes. The tips of their claws were an intense red shading toward orange, and they were fatter and fiercer than the males. A smaller she-crab, with a triangular plate on her abdomen instead of the rounded one that appears at the last moult, followed them and then the males woke from their midday nap and took over again.

By midafternoon the watermen began to pass upriver, heading home in their slender and sturdy boats from a day that began long before first light. "Two-and-a-half," one of them called out; he had spent 12 hours working for a return of perhaps $75, never mind expenses.

Such slim pickings by a man who knew what he was doing made the suburbanites' bag of three dozen crabs - precisely the catch predicted by Schnaitman - seem more respectable. Only one crab had come up undersize all day, and he missed by only an eighth of an inch.

The crabs, most of them bigger than those that pass for No. 1s early in the season, would have cost at least $36 at the Maine Avenue seafood market and probably $45 steamed at a Washington crab house (if you could find one that had crabs). Total expenses were $9 to Schnaitman, $2.50 for the Bay Bridge toll and $5.50 for gas.

"Don't tell anybody about this," the senior suburbanite pleaded. "Let them find their own damn crabs."