Except for a small coterie of fly fishermen who make regular pilgrimages to the fabled limestone trout streams near Carlisle, few area anglers fish much in Pennsylvania. This could be a big mistake.

In about half the time it takes to get to such popular "local" fishing water as Ocean City, Kerr Reservoir, Chincoteague and Deep Creek Lake, you can be wetting a line an any number of fertile lakes, ponds or rivers in the Keystone State.

And that ain't a bad place to be.

Pennsylvania has one of the most sophisticated fishery programs in the country. And it isn't all trout-oriented, as some mistakenly believe. True, 7.3 million trout were stocked in the state last year. But 30 million walleyes, 3 million Amercan shad, 1.5 million salmon and a quarter of a million muskies, among other, were also stocked. Bass grow husky in many of the state's lakes and rivers, and the season on both large-mouths and smallmouths opens at exactly 12:01 a.m. this Saturday.

A brief rundown on a few of Pennsylvania's better waters nearby:

Enough has been written about the classic Pennsylvania limestone trout steams so that anyone who craves this difficult form of fishing should know where to go and what to expect. Briefly, these streams in their "fish-for-fun" stretches offer some of the best fishing in the East for exclusively stream-bred trout. Falling Spring, near Chambersburg, has mainly rainbows; the Letort, near Carlisle, has mostly browns; Big Spring, at Newville, boasts big native brookies in the headwaters, wild browns and rainbows farther downstream.

Bring along spools at 6X and 7X tippet material, a selection of flies including shrimp and sow bug patterns, black and cinnamon ants, olive and sulphur mayflies, a few midge dries and pupae, and you should be on the right track for cracking the code on these clearwater alkaline streams. A large dose of patience also helps immeasurably.

Intriguing as these limestone streams are, they represent only a tiny fraction of Pennsylvania's nearby trout waters. Most of the other streams are freestone. These waters flow in the more typical series of riffles and pools, are less alkaline and are formed by drainage from runoff and feeder creeks rather than springing from a subterranean source at a constant volume and temperature. They are usually less fertile than their limestone counterparts, but provide easier and more productive fishing for the avetage angler - without any sacrifice in beauty.

Franklin County's East Branch of Antie-tam Creek, in the town of Waynesboro, on state Route 16, is one of these splendid little freestoners. It's stocked with browns, and the "fish-for-fun" stretch runs through pastoral Renfrew Park. Black ants, beetles and Adams dry flies work very well on this creek's frisky trout.

Clarks Creek, another lightly fished free-stone creek, has a two-mile fish-for-fun stretch in Dauphin County, north of Harrisburg on Route 325. Thousands of larvae of the destructive gypsy moth should be clinging to the streamside foliage here now. It's a sad sight, since many of the trees will be stripped bare by the relentless munching, but the caterpillars do produce excellent angling: The trout feed greedily on the larvae.

A clipped deer-hair "inchworm" fly in sizes 6 to 10 will draw savage strikes from Clarks' browns, brooks and rainbows when these insects are tumbling into the stream. Use a 5X or 6X tippet and drop the cylindrical pattern to the water with a tiny splat to mimic the behavior of the naturals.

Many of the creeks and rivers snaking through southern Pennsylvania also offer good fishing for bass and panfish. The granddady of all such warmwater rivers is the Susquehanna, which offers fishing on a truly grand scale.

If you're worried about eating fish caught near the site of the Three Mile Island nuclear accident, breathe a sigh of relief. "Tests of fish collected from the Susquehanna River following the nuclear reactor accident have proved there was no radioactive contamination," says Will Johns of the Pennsylvania Fish Commission.

Smallmouth bass, suckers, carp and wall-eye were taken above and below Three Mile Island and tested with equipment flown in after the nuclear incident. Says Johns, "No radioactive Iodine 131 was detected in the fish samples from the Susquehanna River. These tests confirm the fact that fishermen and their families eating any fish caught in the river have nothing to fear."

But they do have plenty to catch, including smallmouths and lesser numbers of largemouths, walleyes, rockbass and blue-gills by the stringerful, plenty of carp and catfish, plus the occasional muskie. The river in this lower stretch is very broad and boats are definitely helpful. The Pennsylvania Fish Commission (Box 1673, Harrisburg 17120) can provide fishing maps and information on access points.

There are also many good areas for wade-fishing the river, particularly above Harrisburg. Tom Baltz, of Boiling Springs, likes to fish the water along U.S. 11/15 between Harrisburg and Marysville with a fly rod and large nymphs. In a typical afternoon he'll catch several dozen bass running up to 15 inches. Spin fishermen connect with minnows, hellgrammites, crankbaits and Mepps spinners. For walleyes, use jigs tipped with minnows or nightcrawlers, and fish right on the bottom.

For lake fishermen, Gifford Pinchot, just northwest of York, is a top choice. There are good-sized crappie, as well as thick bluegills and quite a few northern pike. Take Routes 74 and 177 to reach this lake, about two hours' drive from Washington.

A slightly closer spot for warmwater fishing is Lake Marburg, also known as Codorus. East of Hanover on Route 216, this big lake has been exceptionally productive over the last few years. The crappie, which average two-thirds of a pound, may still be congregated around brushpiles and fallen timber. Later in the summer, fish the bridge pilings for them, where yellow perch and walleyes also turn up. Bass to eight pounds have been taken in Codorus, and muskies and northerns prowl the weed beds in search of easy meals. A fast-trolled plug might be just the morsel to tempt them.

Non-resident Pennsylvania licenses cost $14.50 for the season, $9.50 for a seven-day tourist permit. You can buy them at most sporting-goods stores. CAPTION: Picture, A BROWN TROUT LEAVE ANTIETAM CREEK, A FREESTONE STREAM. By Gerald Almy.