Cornish coast keeps unspoiled image. Sophisticated city life a world away on this seafaring peninsula

`ENGLAND'S Cape Cod'' - there may be other resorts on the British coast that deserve the title. But to this habitu'e of New England's Cape Cod, the cliffs, beaches, and sailing harbors of the south Cornish coast are it. Similarities between the two areas are striking.

Cornwall juts out from the west coast of England as Cape Cod juts out from the east coast of the United States. For the most part, the Industrial Revolution bypassed both of these seafaring peninsulas, with their small cottages and pretty town centers. Separated for centuries from the sophistication of population centers, both Cornwall and Cape Cod have managed to preserve most of their charm and flavor.

To me no area typifies England's Cape Cod more than the one surrounding St. Mawes, opposite Falmouth. The town nestles gently around a sailing harbor, not unlike Chatham or South Dartmouth, Mass., except that the main street tops a concrete quay that runs along the edge of the water.

Balancing Falmouth's larger Pendennis fortress in the distance, a small round castle crowns the St. Mawes headland. It overlooks Carrick Roads, the confluence of estuaries of the River Fal.

Much deeper than the rivers that flow south on Cape Cod, Mass., these estuaries are reminiscent of mini-fjords, flooded valleys. Crossing King Harry Ferry between pleasant hills above St. Mawes - where the Fal has rapidly become quite narrow - one is surprised to see oceangoing ships anchored in storage still farther upstream, where one would expect the river to be much too shallow. Of course, this geological feature is of great advantage to sailors with deep-keeled boats.

From the public coastal footpath - rather like America's Appalachian Trail - that follows the entire Cornish coast, one has dramatic views of the cliffs that surround England's most westerly peninsula: sea- and wind-weathered arches, caves, and rocky promontories that separate one unspoiled beach from another.

Each beach in Cornwall has its own individuality, and most are sandy. Some have automobile access, but the more interesting beaches tend to be reachable only by foot down steep paths. Others are found only by boat, because the descent from the cliffs is too perilous. Since some Cornish fishermen still use glass fishing net floats, smooth, colorful pieces of rounded, broken ``beach glass'' can be collected as free souvenirs of your visit.

Walking on the coastal path should not be missed, whether you descend to a beach or not. Almost any walk will give you the flavor and enjoyment of Cornwall. In many places the main path itself is not particularly rugged.

Try taking a lunch and walking slowly for an hour or so, relishing the views, the wildflowers, and the grasses along the way. Find a pleasant spot to eat, protected from the wind, and perhaps read a few chapters of a Cornwall-sited book like one of the ``Poldark'' series. Then walk slowly back.

Across one small estuary from St. Mawes, the walk east from the parking lot at St. Anthony Head is lovely. After 20 minutes or so, you come to another maintained trail at the edge of a wheat field with uneven steps that lead sharply down to a pleasant beach protected by the National Trust. Since the winds are often from the west, a southern beach like this one will usually be sheltered.

Beyond the natural pleasures of the area, there are day trips to castles like Restormel and the romantic almost-island of St. Michael's Mount near Penzance. Also worth visiting are stately homes such as Lanhydrock, and the large National Trust gardens such as Trelissick, just to the other side of King Harry Ferry.

If you go

Rent a cottage for a week in Cornwall and do your own shopping and cooking. You save money - especially if you are taking your family - and you also learn more about the country. It's likely that a milkman will come by to deliver milk, double cream, and Cornish clotted cream, along with a daily newspaper. Cottages are listed in the catalog ``English Country Cottages.'' Write English Country Cottages Ltd., Claypit Lane, Fakenham, Norfolk, England NR21 8AS.

You'll need a car if you're touring Cornwall, and you might want to consider taking a train or plane to some place like Exeter or Penzance and renting it there. Car reservations with major companies can usually be made, and fees paid at the cheapest rates, from outside England. Don't worry about driving on the left. You'll get the knack of it quickly. Be sure to ask the agency when booking about the cost of additional insurance (which can be very high) and if you can get a refund on the VAT (value-added tax). See if you can get it and any purchases credited back to your credit card.

If you're spending more than two or three weeks, and especially if you might be returning in less than 12 months, consider joining either the National Trust (yearly membership 14.50, about $23) or English Heritage, at any of their sites. The trust holds many of England's ``stately homes,'' natural sites, and magnificent gardens. English Heritage generally holds ancient monuments and castles, including the Tower of London. Entrance to all of their locations is usually free with a membership. Fees can be expensive, as much as 4 (about $7).

If you sail at all, or just want to learn how, go to the St. Mawes Sailing Club on the harbor or Pasco's boatyard at nearby St. Just, and find out how to rent a boat or get sailing lessons.

Inquire, too, about renting a small powerboat like a Zephyr to do a day of exploring up and down the estuaries and perhaps around St. Anthony Head.