Float fishing - drifting with the current, casting to the swirls of feeding bass and bluegills - is a tonic for sensibilities numbed by weeks of pent-up city life.

On a float trip our ability to perceive is renewed as the senses are treated to a succession of delights, and the tone is set at daybreak for events that will unfold throughout the rest of the trip at the perfect pace for assimilation.

Dawn comes slowly, for on most area float-fishing streams you'll likely be camped in the shadows of a tree-cloaked mountain. By the time sunlight edges into your camp, eggs will be frying, coffee brewing and toast browning in a skillet laced with sweet country butter.

It's a tossup as to which is richer; the eyes' feast on the sparkle of dew, or the aromas of woodsmoke wafting on a frail mountain breeze, bacon crackling on the skillet and coffee steaming in tin mugs. And the taste of this breakfast is more delightful than it ever can be in a kitchen.

Nor are the ears neglected: Birds chime in with their caroling, a squirrel chatters at the strangers under his favorite hickory tree and, reminding you why you're there, a smallmouth punctures the stream's surface as he leaps at a fluttering damselfly.

Break camp and load the canoe, and with a crisp stroke of the paddle you are drifting at the perfect pace to cast your tiny spinners and plugs at waiting smallmouths. In minutes the tactile delight of a fish throbbing on your line is there, completing the circle of sensory delights.

But soon enough the pragmatic reasons for float fishing become apparent. You are on the water at dawn - something you could never manage if it meant waking up in the city at 3 a.m. and driving two hours to launch your boat in the early-morning fog. And something would be missing, too, even if you could accomplish the task: Somehow the day never feels as complete as when you awaken on a misty riverbank.

Having drifted and paddled for several miles the previous afternoon, you're far from the roads, away from the hard-fished easily accessible water. The chunky small-mouths, colorful redbreasts and plodding goggle-eyes here have seen few artificials, and are far more eager to jump on your offering than their cousins in pools close to roads.

Strikes come on virtually every other cast with the 1/16-ounce spinnerbaits. They are mostly panfish, but fat ones that buck hard against the light rod. With Rapalas and Rebels, you draw maybe half as many hits, but they are solid and strong, and smallmouths of 15 inches are sometimes dangling from the end of the mono when you pump the resisting quarry to the boat.

It's the fly rod that you turn to most, though, reveling in the grace and beauty of the peach-colored line slicing through the clear mountain air. Takes come often as sunfish and bass pounce on the undulating marabou streamer, catapulting through the surface and landing with a flop that sprays water droplets like a circle of gems.

You will cover many miles with the float-fishing methods and many different types of water. It will enable you to find a pattern: spinners in riffles, Rapalas along the shore, poppers in the backwaters - whatever strikes the whim of the fish on any given day. After testing the tastes of the fish, you can concentrate on the most productive types of water with the best lures and retrieves.

It's a satisfying form of fishing, both for the nerve-frayed city-dweller needing to revive his senses and for the hardcore angler who likes the increased catches.

Planning is the key, and the first step is to pick a good river. Top candidates in terms of scenics and lively fishing include the Rappahannock, Rapidan, James and Shenandoah in Virginia; the Cacapon and Potomac in West Virginia; the Susquehanna in Pennsylvania; the Monocacy and Potomac in Maryland.

After choosing a river, isolate a stretch you'd like to float and get topographical maps for that area from the U.S. Geological Survey, Map Distribution Office, 1200 South Eads Street, Arlington. These will show most rapids, dams and other hazards you should be aware of, and pinpoint landmarks that should allow you to gauge the speed of your trip as it proceeds. This will enable you to arrive at the take-out point just when you want to, rather than a day early or a day late.

The mistake novices are most prone to make is biting off too large a section of river. To fish a stretch of water thoroughly, paddle leisurely through slow sections and stop for a relaxing lunch, choose about half of what your first impulse suggests. Particularly misleading are road maps that make a long, circuitous stretch of river look like a short straight shot to the next access area.

Normally, you'll want to anchor and wade some of the better-looking areas and paddle through shallow barren stretches. Given this approach, a good rule of thumb is to plan on one mile per hour, gauging from an accurate map. If you think all the water will be good and fishable, choose a trip calling for only half a mile per hour.

Johnboats are fine if the trip doesn't have any long, currentless stretches or tricky rapids. Most float-fishing specialists, however, have settled on the 17-foot shoe-keel Grumman canoe as the top craft. They are rugged, hold nearly half a ton of cargo, negotiate mild whitewater well and are great for paddling through slow water.

Gear for float fishing should include sleeping bags wrapped in waterproof bags (trash bags will do), extra clothes, food, cooking gear, tackle, flashlight, lantern, first-aid kit and a ground tarp or tent.

The safest approach or float trips is to take two vehicles. Leave one car at the takeout point and use the other one to get the boat, fishermen and gear to the put-in point. Some adventurous types go in one vehicle and try to catch a ride back to the car before or after the float. This approach can't be recommended, though - as soon as you start looking for a ride back to the car along these back-country roads, vehicles become depressingly scarce. CAPTION: Picture, DRIFTING DOWN THE STREAM AFTER THE TUG OF A FISH. By James M. Thresher.