SOME 12,000 Plain People, descendants of those attracted by William Penn's Noble Experiment, make their home within a 30-mile radius of Lancaster, Pa., living and working in an enclosed world that has never accepted electricity, the automobile or the relaxed behavior of modern society. a

Since the rest of us have a hard time imagining what it is like in such a world, the Pennsylvania Dutch have become an enormous tourist draw.

The Mennonites -- and their even more conservative offshoot sect, the Amish -- are very much in evidence driving their horse-drawn carriages in the vicinity of Bird-in-Hand, Intercourse and other small towns of the region, but they avoid tourists as much as possible. It is next to impossible to scrape acquaintance with them, nor can you snap their picture since they take quite literally the Bible warning against graven images. Presumable they have become used to being stared at by bus loads of visitors, but one wonders how they feel about replicas of themselves in traditional dress beckoning customers into gift shops and fast-food places.

Yet with all its traffic and unabashed commercialism, the Penn-Dutch country offers interesting sights and some of the most beautiful landscapes this side of New England. Get off terrible, traffic-choked Rte. 30 east to the narrow country roads through the fields, and you'll fall in love with the fertile farm country that brought the Amish here. Pick up a map of the region from the Visitors Bureau, at 1799 Hempstead Rd., and let them help you chart your course.

You must, of course, look at the farmers' markets which offer for sale the produce of this rich land. Their open days vary, but Saturday is a good bet for most. I chose the Meadowbrook Market, five miles northeast of Lancaster on Rte. 23, because it was handy.

Outside, the Meadowbrook is nothing, an unimposing brick building with a mammoth parking lot. Inside, it is a smorgasbord of all the things for which the area is famous -- homemade noodles, pretzels, fresh sausage, scrapple, Muscovy ducks, pigs' feet made into souse, and, of course, shoofly pie -- obligatory for visitors and handy to transport, since it requires no refrigeration.

I saw the market in early March when nothin local could be offered from the fields, but I was assured that in late April the asparagus and spinach would be leading the way for a parade of vegetables and fruits to make Florida blush.

The inevitable tacky ceramics are offered here as well, and the antiques on the floor below are pretty well limited to tinware, stoneware, chests and hex signs. You'll find no undiscovered bargains here. They know what prices golden oak is bringing in the cities and they have enlarged the definition of antiques to a point which gives one pause. I saw a WWII Army Air Force major's uniform here offered for sale at $28.

With the shoofly pie in my car trunk, I turned north on Rte. 222 to Ephrata (say F-rah-ta) where another German settler, Conrad Beissel, established a religious community in 1732. The cloisters remain today where he built them 250 years ago, a monument to the beauty of simplicity and an outstanding example of medieval architecture in this country. Most of the old weathered buildings are open for wandering through, though the main meeting house and the room where travelers were put up are seen only with a guide. Tours go frequently.

The calligraphy display in the visitor's center is as beautiful as old lace, and the buildings beyond as cold and ascetic as you might expect of an order which slept on wooden pillows and were often barefoot. The sisters, we are told, retired at 9 but were roused at midnight for more prayers. The average woman's height at the time was 4 foot 10, and the doors throughout are very low, not only to suit the sisters' small stature but to encourage humility.

In the end, the life of sacrifice was the undoing of the community, which was wiped out by typhus contracted from the soldiers they nursed after the battle of Brandywine.

If you want the total experience of the Amish country, you can eat at any number of restaurants featuring their hearty style of food, in most cases sitting at a long table with other guests. The Good 'n' Plenty Restaurant on Rte. 896 is an example where Dutch dining includes the works -- ham, veal, chicken, sauerkraut, pork, several kinds of bread and potatoes, apple butter, relishes, hot bread, pies and cakes -- a family restaurant you should try if you haven't. Closed Sundays.

Thinking to branch out a bit, I elected to motor to East Petersburg and sample the food at Hayden Zug's, of which many speak highly. Zug was a German immigrant who, back in the 1920s, bought the old hotel from which the restaurant evolved. The hotel was once a prosperous midway stopping point on the dirt track between Lancaster and Lebanon, and has progressed over the years from hotel to general store and now to a dark, attractively appointed restaurant serving vaguely French food. If you want a recess from things Amish, this is rather fun. Reasonable by our outrageous city standards.

Most interesting of all would be to visit an Amish farm, but since this is not possible, next best is to explore their culture via one of the three recreations in the area. I selected the Amish Farm and House, six miles east of Lancaster on U.S. 30, and came away with my curiosity about the sect whetted by the very professional tour through the house. The guides can't all be as good as Betty Idou, who was on duty the day I saw the house, but the information must be the same and it vastly adds to your enjoyment of the area.

The house is an 1805 stone structure with the typical large kitchen that is the heart of the Amish family, a place for studying, cooking, even sewing and reading The Budget, the Amish newspaper. Hostesses show you the sober dresses, bonnets and hats hanging on the walls, the sparsely furnished bedrooms with the cradle beside the biggest bed. You also get a fascinating peek into the problems of the old order in holding the young within its strict sect.

The young Amish apparently occasionally kick over the traces and drive the horse and buggy to a motel, where they hire a room to look at television and, clued in by what they see, turn up the sides of their traditional black hats to ape the current "Dallas" fashion. Many postpone their baptism into the religion until their mid-20s, by which time, if we are to believe what we are told, they have put all doubts behind them.

The lecture tour makes these aloof, sober-faced people far more interesting, and the more unimportant the details, the more the crowds hang on the guide's words. What is more entertaining than to know that all Amish women part their hair in the middle and that Mennonite buggies are gray and Amish black?

Lancaster County abounds in chain motels that line the roads and seem a little out of place in a country with 30 covered bridges. You might prefer the General Sutter Inn in Lititz, which is between Ephrata and East Petersburg on Rte. 501. This is an old-fashioned country hotel, plain and reasonable, though straining a bit to gussie itself up in the lobby and dining room. No elegant hostelry, but a nice change. The Sturgis Pretzel House, billed as the oldest pretzel bakery in America, is in Lititz.

The Plain People are all very well but, since you're near, you might want to drive up to nearby Hershey for a quick trip to Chocolate Town. Prices for the summer season went into effect March 30, but the crowds have not yet made the lines at Chocolate World irksome and the Hershey Gardens are already open.

New this year are a miniature rose garden and a garden of ornamental grasses which have been added to the famous Hershey Gardens. There's also a living fence of roses along Hotel Hershey Road, all scheduled to burst into bloom later in the season.

Hershey Park doesn't open till next month, but when it does it will be only the second year for a real killer called the Pirat, a giant ship that swings in a 75-foot arc and drops you back in place with almost all of your stomach intact. The arguments these days are whether this is more hairy than the equally new Cyclops, a centrifugal ferris wheel. The new kiddies' area will be open in May, and don't try to get in without a child.

June 2, the Treasure of Conception, relics from the Spanish galleon that sank more than 350 years ago, will be shown at Hershey's Museum of American Life. Pieces of eight, gold chains, silver table settings, pottery and rare Chinese Ming porcelain estimated to be worth more than $40 million were brought up from the briny in 1978, and a large sample will be in Hershey since the discoverer, Burt Webber, is a Pennsylvanian.

The Concepcion, packed to the hilt with these pretties, sprang a leak in a hurricane in 1641 and, in an attempt to return to land, struck a coral reef about 80 miles off the Dominican Republic. Many a wealthy shipwreck victim sank to his death weighted down by by his wealth and his chains which were dredged up centuries later for our edification. Tobacco sticks and silver bases for coconut cups (coconut was a curiosity to Europeans) were also found and -- what could be more suitable? -- a chocolate frother to mix chocolate, water and sugar for Europeans just getting addicted to the New World sweet.

IF YOU DRIVE: It's easy to get to the Pennsylvania Dutch country from Washington if you follow I-95 to Baltimore's Beltway (695), turning north toward Towson, and pick up Rte. 81 to York. From there take 30 east to Lancaster.