This time of year, the most strenuous leisure activity for many is tilting an iced drink in an air-conditioned room.Not fishermen, though. Few anglers have the restraint to simply sit back and wait for the sticky weather to end in September.

Still, for the rest of this month and much of next, staying at least moderately cool while fishing is important. A dripping brow saps the energy and concentration our sport demands; with gamefish as reluctant as they are to bite in hot weather anyway, any letup can be the small excuse they need not to strike at all.

Hot-weather fishing can be dangerous: Heatstroke, sun stroke, dehydration and severe sunburns are possibilities.

Clothing is the first thing to consider. Bridal white is impractical for most types of fishing, where getting a bit messy is inevitable. Cotton or cotton-polyester in a light khaki is excellent: Light enough to keep you cool, yet dark enough not to look filthy the first time worm-stained hands touch them.

Shorts are okay if you aren't going to be walking through brush or wading; if you are, the extra protection long pants offer is worth having. If you haven't gradually tanned your legs, however, it's wise to avoid prolonged exposure to the sun.

The head deserves special attention, and the avid angler who doesn't war a hat is asking for trouble in the form of skin cancer.

If the danger seems far-fetched, Bob Stearns (in the July issue of Outdoor Life) will convince you otherwise. The ubiquitous baseball type hat will keep the sun off your face and out of your eyes, but it won't protect the tips of the ears - prime spots for skin cancer to develop. Topless tennis-type hats are better, since they let body heat escape through the crown; but they, too, fail to protect the ears. Hats made for saltwater fishing, with long visors in the front and light canvas earflaps, are best of all.

Suntan lotions are useless for protection, but sunscreens can cut out over 90 percent of the harmful ultraviolet rays while still letting the short rays get through and tan you. Look for the active ingredient PABA on the label, and apply the screen to the face, hands and neck or other exposed areas of the body whenever on the water for long.

Dehydration is another danger; drinking plenty of water, fruit juice or Gatorade will quench the thirst and restore body fluids lost through perspiration.

Another way to beat the heat is to choose trips that naturally tend to keep you cool. One August ordeal I rarely let myself be talked into anymore is midday farmpond fishing from a metal johnboat. You fry like bacon in such a setup. Worse yet, the fish rarely bite well. The steaming cauldron of a pond slows them down as much as it ought to do to any sensible angler. I've been in situations like this where the boat got so hot at noon that you could burn your skin by touching it. Fishing degenerates into a chore.

But return to this same pond anytime from about seven in the evening through eight or nine the next morning and it's another world. When the sun sinks behind shoreline trees, owls screech and frogs start bellowing, a breath of coolness spreads over the waters. Insects hatch, minnows fin to the shallows, and gamefish begin to feed. Big predatory bass, trout and catfish are active at this time, and the temperatures make it a pleasure to go after them.

Fishing in the dark takes some getting used to, but once you make the transition you may be a convert, giving up the lure of daylight angling altogether. It's a rare chance for touch, smell and hearing to take precedence over the dominant sense of sight.

Another option is wet-wading a smallmouth river. The Shenandoah, Potomac, Cacapon, Monocacy, James, Susquehanna, Rappahannock, Rapaidan and Rivanna are just a few of the more popular bronzeback waters that bounce down rocky streambeds not too long a drive from Washington. Water in the 70s or low 80s lapping at you does much to relieve the bite of 90-degree air temperatures. Wear lightweight pants and socks, and an old pair of sneakers. Shorts don't offer enough protection; jeans are rough and chafing and hold too much water to be comfortable.

No need for a huge tackle box on these trips: Either wear a trout fishing vest and stuff your lures in it, or sew a few extra pockets on an old shirt that you can use specifically for this type of fishing. Repalas, Rebels, Beetle Spins, Mepps and a few curly-tailed grubs or marabou jigs will do nicely when cast with an ultralight spinning outfit on 4- or 6-pound line. Work the eddies below riffles, pocketwater behind bolders, deep pools and shorelines for an assortment of smallmouths, rockbass, bluegills and redbreast sunfish. This fishing is sure to knock the hurt out of the heat.

A final way to combat summer heat is to hike into one of the 40-odd trout streams churning down the slopes of the Blue Ridge Mountains in Shenandoah National Park. Almost all of these streams have thriving populations of native brookies, and the only way to reach them is with a one- to three-hour hike. You can trek down from Skyline Drive to most of them, or forge up from backcountry roads. The upper reaches offer the best fishing.

Don't expect any giants; a 12-incher is a very good fish here. You'll have to work hard to take fish over the eight-inch minimum, but it's often possible to catch as many as 20 or 30 small trout in a leisurely afternoon. The sparkle and life of these colorful trout makes it a rare pleasure, even if most are tiny. Lofty pines, spruce and smaller dogwoods and elms provide a rich canopy of shade; coupled with the elevation, it makes the park streams lovely and cool on all but the most brutally hot days.

To fully tap the pleasure of these streams, get a back-country camping permit from a park office, take along a skillet and sleeping bag and make it an overnighter. You'll have a hard time remembering what it was like back in the blistering, muggy city. CAPTION: Picture, SMALLMOUTH BASS, REDBREAST SUNFISH, CRAPPIE AND ROCK BASS, AND TWO FRIENDS. By Gerald Almy.