YOU CAN FIND Muddy Creek Forks on the Pennsylvania maps but there's no easy way to get there. The same goes for Conventryville in Chester County. Country roads that are no more than a thin gray thread in Rand McNally twist and turn and hump and finally deliver you, in their own good time, to this rural part of the world. It's as if the road builders knew city folk must learn to decompress before they arrive in country Pennsylvania.

But such delights once you do arrive! And each more difficult to find than the last: Hopewell Village, a 19th-century re-creation; a country inn with four stars from the Mobile Guide; a 1730 farmhouse now a "bed and breakfast" in a region where the tax deficit is not so important as the health of baby lambs--these are the rewards for back-road pioneers.

You might even learn to take the time to enjoy a sunset.

Two caveats. Eat a big breakfast before departing and, when you get there, fill the gas tank at the first opportunity. Eating places are as sparse as bluebirds here unless you crash a church supper, and gas-station owners are inclined to go home for lunch Saturday and stay there until Monday. Also, don't count on making telephone calls. The Chester-Montgomery-York counties public phone booths mostly do not work. They swallow dimes and remain relentlessly silent.

No matter. This is the kind of country you can lean your eye against. But first you must eat, because the map may say it's only 150 miles to Hopewell Village, but actually it takes a lifetime (including time out for phoning for directions).

Eat when you get there at the Coventry Tearoom in Coventryville. This is a pleasant country restaurant with costumed waitresses dispensing good light food. Fresh flowers nod on every table and a Bach bourre'e is open on the upright piano. The chicken salad is splendid and so is the cake. You will like the Coventry Tearoom.

Thus fortified, you can enjoy Hopewell Village, just down the road on Pa. 345. This is a Christmas card of a village, which the National Park Service has restored--a wonderful look back to what it was like to live in a tiny industrial town built around a massive iron furnace. The village had a long career beginning with the Revolution, but the Park Service has re-created it as it was during its 19th-century days when a strictly structured society dependent on the flickering red glow of the blast furnace lived day and night with the roar of the flames in its ears.

You can visit the Great House where the owner lived, and the company store where the workers got cotton bolts, flour and coffee instead of cash wages. You can even see the casting house where the molten iron flowed. Hopewell, a National Historic Site, is well presented, with voices (activated by pressing buttons) describing life in the time, complaining about the dust, telling the hardship of a widow's life or of the work of the children. The big mill wheel which powered the blast machinery still turns, complaining at every revolution, and inside a slide program explains it all from the status of the village clerk to that of the lowliest worker. It's all peacefully rural, a miniature slice of 19th-century industrial life.

Because we planned to cross the Susquehanna River into York County to spend the night at the Spring House, we booked dinner at 5 o'clock at the Coventry Forge Inn. The Forge, on Pa. 23 in Coventryville, has been rated one of the 103 Great Restaurants of America and awarded four stars by Mobil.

Dinner here, needless to say, is a production, and our waiter confided that Wallis Callahan, owner-chef, has stopped serving lunch because visitors wanted to get in and out in an hour or two, thus violating his conception of a meal as an event. Dinner, of course, is splendid--five wonderful courses on Saturday at a special prix fixe of $23. Reservations are a must. Call 215--469-6222.

The inn was built in 1717, 15 years before George Washington was born, and the old buttonwood tree on the lawn beyond the porch where you dine could not be encircled by two, perhaps three, men joining hands. The Forge takes a few guests overnight in its separate guest house, but you will have to make plans way ahead.

"Take 23 to Lancaster, cross the river at Columbia and turn south by the river," directed our waiter when we asked for help in getting to Muddy Creek Forks. After that we were alone with our apprehension, our map and the gathering darkness.

No trouble crossing the river but by that time it was dark. The phone booths did not work and the people in the Farm Stores, which are the only lighted buildings in rural Pennsylvania after dusk, whispered with respect that Muddy Creek was a far piece, almost to the Maryland border. We lost the road, cursed the darkness and persevered. Two hours later we finally nosed our little car into the dirt road in front of the Spring House and stumbled up the old stairs.

The Spring House, home of Ray Hearne, is a 1730 stone farm house that she opened last year to overnight guests. All small inns reflect the personality of their innkeepers but the Spring House is Ray Hearne. From the coal-burning stove on which she cooks like a virtuoso to the spare whitewashed walls and bouquets of wild flowers from the garden, the inn shines with the good taste of this gentle young Quaker woman with an Antioch education. Surrounded by three cats and her spaniel, Hadrian, she presides over a three-room, share-the-bath, bed and breakfast with the presence of royalty.

Bed and breakfast? Technically, yes. When we arrived, she had just put a full dinner before a young couple who were occupying the south bedroom. Remember, I told you there were no restaurants in this countryside. She was feeding them, but dinner is not in the bargain. You who understand the territory should eat before you come.

At night we slept under Amish patchwork quilts beside pot-bellied wood stoves, now cold but surely handy for wintertime guests. In the morning Ray shuttled between the turn-of-the-century gas stove she has installed on the covered patio and her coal-burning wonder in the kitchen. From the gas antique she turned out scrambled eggs, yellow as daffodils as they always are from free-ranging chickens, and pork sausage from a neighbor's pig.

From the coal-fed monster she produced her own stone-ground wheat bread, with grape or wild strawberry jam, and blueberry buckle, all topped off with orange juice and coffee. Tachyon (faster than the speed of light), her tom, watched with yellow eyes as she tested the temperature of the oven with her hand. The night before, Ray told me, she had made an angel food cake in this old oven.

We had planned to go home early but, caught by the charm of Muddy Creek, lingered on. The smell of the wood fire in the fireplace and the wonderful aroma of baking bread filled the room as we dawdled over coffee to hear about life in the country. Neighbors are neighbors here in Muddy Creek. Ray buys her flour for 14 cents a pound at Rohrers Mill and, if nobody is there, leaves the money under the pad of paper.

In 1730, Muddy Creek Forks was an agricultural center, a bustling community with a creamery, a cannery and a knitting mill. Muddy Creek died with the Maryland and Pennsylvania Railroad, familiarly known as Ma and Pa, the railroad on which the drummers from Philadelphia once arrived, hired a horse and buggy and fanned out to sell their wares. Now the tracks are deserted, the roads unpaved and largely without signs, and God help you if you don't have directions.

You imagine there might not be anything much to do in Muddy Creek? Shame on you.

We walked up the Down Road to call on the Blanchards, neighbors who showed us around their sheep pens, introduced us to their new prize Corridale lambs and invited us in for an organ concert of hymns. Mrs. Blanchard collects organs. She has three in the living room of their stone farmhouse and has her eye on another. You should hear ''Guide Thou Our Steps'' on the Gothic ex-church organ. Afterward, we walked down to the creek and picked some fresh watercress. It's a glimpse of a world that makes you wonder why we spend our lives in rush-hour traffic.

If you're a wine buff, the Allegro vineyard, whose 1980 Cabernet Sauvignon has just won the Eastern Wine Competition award, is nearby. With tax, this wine costs more than $9, but then it's certainly a splendid wine.

Call (717) 927-6906 for reservations at the Spring House. When you call Ray, tell her I'll be back one of these days. Tell her I love her garden, guarded by ancient griffins that look as if worms had nibbled them. Tell her I love her stove and the way the moon came in my window and lit up her selection of pottery and carefully mended old china on the sill.

And be sure to ask her for directions.