I was surprised, pleased -- and embarrassed -- to loom large in Hank Burchard's excellent article "So You Want to Learn Canoeing" [Weekend, July 20]. The shift from flat-water to white-water canoeing is, indeed, entering an entirely new field of paddling -- well worth learning in organized classes.

My embarrassment stems from my costume -- or lack of it. Neither I nor any experienced white-water paddlers I know now paddle without wearing a life jacket. In an upset a loose jacket in the canoe just floats away uselessly. Jim Thresher must have caught me demonstrating a paddle stroke. JOHN SEABURY THOMPSON Chevy Chose.

WAITING FOR GAS

Thank you 50 times for Rozanne Weissman's wonderful piece [Weekend, June 29]. It almost made waiting in line for gas bearable. . .LEE EDWARDS. Washington

SPEAKING OF TROUT

Perhaps Jack Scanlon is rankled by Patuxent poachers [Weekend, June 29], but a few of us locals have some ranklements of our own.

How long has Jack fished the Patuxent? Does he remember the upstream stretches as they were only six years ago, with emerald clear waters and a solid rock bottom? Does he remember the teeming trout that swarmed in the crystal pools?

They are gone now, but not by poachers. They are unable to survive a stream that is now choking in the silt of Damascus development. The upper Patuxent is ruined, all right. The culprit: developers.

Incidentally, as many trout poachermen take their booty on flies as on worms.

Once upon a time there was a secret trout stream right in the heart of suburbia.

A tiny creek with deep tree-root holes, the browns it contained were beautiful jewels, beheld only by the few who knew.

Having first seen the specimens in 1960, at the tender age of eight, I later finished this wonderful creek exactly three times per year. Setting myself a two-fish limit per trip, I released all over 14 inches long, thinking to ensure their survival. I released more than I kept always.

Come spring 1977, someone foolishly let slip the secret of Paint Branch; in a Post article bearing the news of the Northwest Branch stocking, all the meat fishermen were set adrool by the revelation of Paint Branch trout. Within one month every beautiful pool, every difficult pool had had its protective layer of overgrowth shorn back by clippers.Every little path was muddy with wader tracks and trashed.The population of innocent little beauties was utterly decimated. Needless to say, I still am sick over the loss of such a rarity.

There are other streams in Maryland that contain wild trout, unlisted in the sportfishing guide. When and if you stumble onto another, kindly refrain from supplying the trout-hungry populace with its location. I plead for the lives of little trout. . .J.P. Smith Silver Spring.