From spring through fall powerboats swarm Chesapeake Bay and its tidewater rivers. The boats cost what houses once brought and burn gas the way Cadillacs used to; it seems unlikely that American-Style powerboating can long survive both inflation and the energy crisis.

There is an alternative. There are graceful and shapely saltwater craft that are cheap, burn on fuel, foul no air and never break down. The Indians called them canoes.

The canoe is not, of course, a blue-water boat, although one that is skillfully handled can weather surprisingly rough seas. There are even enthusiasts who shoot the surf in them, getting brief but exciting Nantucket sleighrides.

But neither is the typical powerboat suitable for any but the most moderate sea, as the U.S. Coast Guard keeps telling us. It is the limitations of the canoe that make it particularly suitable for use on the thousands of square miles of backbays and marsh within a one-tank round trip from Washington. The little boat won't go far or fast enough to get you into trouble; and the canoeist, diddling along, sees places, birds and beasts that the powerboater blasts past.

Viewed from a speeding boat in a channel, the marsh seems almost deserted. Birds wheel above a flat expanse of gray-green grass. From a canoe, gliding through a narrow "gut," the marsh is seen to boil with life. As you round a bend, startled terrapins slip into the water from their sunning banks and a rail bird bursts into clumsy flight from a clump of grass you wouldn't think would hide a fly. At second glance the clump is seen to have a snail or two on every stalk, along with odd-looking insects. Crabs go skittering and muskrats scamper. The fish are there also, looking for food, peace and quiet.

A canoeist willing to try to think like a fish - remaining patient, watchful and always mindful of weather and tide - can feed the belly as well as the spirit. A dip net should always be ready to hand. Oyster bars abound; the big ones are all private or leased - and marked - but there is no end of small ones where the shellfish are free for the gathering. (Never mind the "R" months, oysters are edible year-round). Mudflats and sandbars will usually yield clams and often whelks. Marshes and river margins also abound in edible plants, so a wild-foods guide is invaluable.

Resolute canoe-campers can be as alone as they like on any of hundreds of uninhabited islands that dot the rivers and marshes. The price of admission is some paddling, some forethought and complete camping equipment plus first-class lifejackets and extra clothing that will keep you warm in the wind though wet. Other necessities include the latest large-scale map, tide tables, plenty of water, insect repellant, a compass and signaling devices if you are planning to go any distance at all from the mainland, and the best local advice available.

For an extended trip the list of necessities is lengthier still, but the way to get into saltwater canoeing is daytripping from a base on shore, preferably in an area you already know. The put-in point and the length of the trip should be dictated by the weather, the tide and the amount of experience the canoeist has. In many places as little as a quarter-mile of paddling will take one into virtual solitude.

The most important thing to take along is the appropriate frame of mind. Sailors will adjust to saltwater canoeing more quickly than powerboaters because they already know about wind and tide, but the alteration of scale will be no less dramatic. Distance over water is more usefully measured in terms of time, and the range of the canoe is extremely limited.

It's because the canoeist must "go with the flow" that the experience is so rich. Yielding to natural forces, moving slowly and quietly, one fits into the pattern of the creatures of the marsh. Canoes don't spook wildlife half so quickly as powerboats, partly because they are not so big and noisy but mainly because they do not exceed the natural pace nor go against the grain.

Not all canoes are suitable for saltwater. Canvas-covered or laminated-wood boats are likely to be seriously damaged by the oyster shells usually found in the little marsh "creeks" that are the most interesting. The razor-edged bivalves also will scar ABS-Royalex type hulls, but so does everything else; it does not seem to affect performance. Aluminum canoes are fine except that they tend to screech like owls when pushing through grass or over shells. Almost any type of canoe can be rented from area outfitters and all can be strapped atop a car, with or without a luggage rack.

A canoe will ride appreciably higher in saltwater, but that is not a reason to load it down. Quartering across choppy water will sometimes be necessary, and the more freeboard the better. Two adults plus 50 pounds or so is about all you want.

Not only will a canoe penetrate shallows no powerboat can pass, at flood tide you can go cross-country, shortcutting the sinuous creeks and flushing marsh hens and other creatures that hide in the grass. But keep an eye on the tide, because dragging a stranded canoe over muddy marsh is exhausting. Time it right and you can ride the tide both ways, or at least catch the slack.

What it lacks in range the canoe more than makes up in mobility. It can be launched and recovered from almost any place that can be reached on foot. And many wildlife refuge managers will permit visitors with a good reason - such as serious birders - to use a canoe in areas where powerboats are absolutely forbidden. The Assateague National Seashore even has three campsites reserved for canoeists.

But the canoeist needs nothing but public waters and public marsh. One four-hour trip this spring, which began and ended at the free public boat ramp in Chincoteague, yielded two semi-serious birders six new species for their life lists, plus terrapins and all the oysters they could eat. A fishing pole and a somewhat larger net would have brought in an embarrassment of riches.

Counting only the birds that passed or stayed within 10 yards of the canoe, they saw: short-billed dowitchers, willets, ruddy turnstones, black-bellied plovers, American oystercatchers, a clapper rail, common terms, laughing and herring gulls, snowy egrets, red-winged blackbirds, dunlins, common crows and boat-tailed grackles. Some of them, as though curious about the unusual craft, repeatedly passed or hovered virtually at arm's length.

Beaching the canoe where they pleased, the pair wandered the shallows and the high marsh at will, as alone as though they were in a world made new (and had to drag the boat a hundred yards though sucking mud when they forgot about the tide). They are people who take pains to tread lightly upon this earth: It comforted them to know that the next high tide would erase all signs of their passage.

And at no point were they more than a mile from their place of beginning. CAPTION: Picture, MOVING IN A CANOE, AT NATURE'S PACE AND ON NATURE'S SCALE, GETS YOU CLOSER TO THE WILDLIFE. By Hank Burchard.