As long as clusters of trees have been "the woods," there have been people who can't be kept out of them. With the unsettling awareness of "ecology" and the awful possibilities of no more woods, a lot of people now find it necessary to wander off pavement into greenery. And, too often, don't know what to do once they get there.

Too many attempt to have both environments, taking along as much of the city as they can in coolers and baskets and backpacks. Others view the land as a challenge, seeking to test themselves. A few are at ease and have the grace to learn something about the state that attracts them.

Some botanize, seeking varieties of fern and flower. Some trek after fungi, musing over chanterelle, morel and puffball. Some peruse rock. Some search for butterflies. Others demand a subject active in every season, present in any environment, a subject obvious but elusive - they find their intrigue in birds.

The rudimentary amateur ornithologist, the basic bird watcher, has an even more basic response to why:

"It's a marvelous excuse to go poking around in the woods."

But, as with any activity in the woods, there are no guarantees that each day will be a joy.

The small expedition entered the woods in mid-afternoon. A Sunday sun had never appeared; dull layers of clouds threatened precipitation over the line of bent heads threading a path down into the lower portion of the ravine.

The modest crew of four was on a special last outing of a winter bird census. Though the season was officially over, spring had not yet thrust forth with a tangle of greenness in the woods, and, until it did, the counting could continue. More importantly, a report of a screech owl needed confirmation.

The outing could even have significance. Such small annual censuses have accumulated startling data. A diminishing robin count on one college campus was the seed of interest which grew into the national alarm over the effects of the pesticide DDT.

Nevertheless, these woods might have seemed small and unimportant to an unknowing observer, Glover-Archbold Park being a mere slash of unkept ground in Northwest Washington. Its edges are trashed, its interior trysted.

The crew had no time for ground-bound errors. They were birders, intent on higher things-the bird census and a relcusive screech owl in an identified hole in a specific tree. So they brought a new tape recorder loaded with the sounds of one of his brothers to rouse him from slumber.

Birding was once a more grisly occupation. In the early days of American ornithology budding naturalists went to the woods with shotguns instead of tape recorders and binoculars. Good aim was as important as experience. The expert collected hundreds of carcasses for study and exhibition.

The amateur ornithologist now limits himself to seeing and identifying wild birds. Ethics forbid he disturb the prey.

But the sport is still a matter of numbers. Status is larely measured in the rarity of species the enthusiast has logged on his or her "life list." The eager beginner must not only study bird guides and be ready to make a positive identification on the spot as a multicolored beast flits across the field of his binoculars or perches on the wrong side of a distant branch, he must be perpared to bear up under the supercilious snears of the more experienced when he announces that his life list is up to 36.

A good look at the screech owl would add a new species for each member of the crew.

G.T. Hunt, a young lawyer in an old black overcoat and a knit cap, led the way down the trail toward the screech owl, reluctantly waiting at each stop while the crew identified and counted birds. The winter census, a 20-year-old project of Shirley Briggs of Bethesda, has noted the presence of 64 different species of birds at different times in a select 35-acre tract of the park.

The winter census has proven there is a relatively stable population of birds in the park. But the related summer census of birds that breed in the park has shown a sharp decline in the insectivorous birds that winter in South and Central Amercia. Where once 16 pairs of warblers used the park each year, none return.

Schreech owls had been regular residents in Glover-Archbold, reported every year until this. Neverthless, there had been a late report.

A stranger encountered in the park had told G. T. and Susan Hunt that he had seen the owl. The couple had spent several vigils staring through their binoculars at a small wounded tree with the designated hole in its side. They had watched through a late afternoon until the light had gone, waiting for the bird to exit on its dark hunting trips. They had arrived in the bleak hours of morning in hopes of seeing it return to its nest.

The top of the bird's head was sometimes apparent in the scarred tree, but its motion was suspect. The birders' strained eyes and trembling hands could be the cause, not the fast beating pulse of a small raptor. The purported owl, in any case, had not revealed itself in full.

G. T. had come late to birding, acquiring the sport when he married Susan four years ago. "It came with the territory," he says. Susan has been interested in birds since childhook and has been a serious birder since college. She was the expert of the crew. She had to confirm each bird's identification before it could be recorded officailly on Shirley Brigg's form, a mimeographed chart of the area.

G. T. carried the map on a clipboard strung around his neck on a lanyard. He marked each bird location on the paper with a small dot and drew a line from it to the wide margins where the number and species were recorded.

As the crew progressed slowly toward the tree of the screech owl, G. T. no longer bothered to earch the canopy of the woods with his own binoculars. He left that to the others and only dotted and lined the notes as Susan reported the end of the arguments.

"What kind of bird is that fat one over there?" asked a blond bearded novice birder.

"Which one?" responded Susan.

G. T. stood a few paces down the path, binoculars and clipboard hanging limply from his neck, his bare hands hidden inside his coat, as he patiently waited for the statistics.He was ready for the owl.

"They sit like that when they're cold," Susan said. "They fluff up their feathers to keep warm. Oh, I see it. It's some sort of sparrow."

"It doesn't look like a sparrow."

The bird watched the crew with suspicion. It faced them, revealing only a round silvery gray breast and a point of beak below a beady eye.

The birders shuffled for position.

"It has some stripes on the side fo its head," said the novice. "But I can't get a good look at them. It keeps turning its head the wrong way."

"It's a white-throated sparrow," decided Susan.

"But I don't see any white throat."

"You can't because of the way it's sitting. It has the yellow mark, though. It's definitely a white-throated sparrow."

The fat little bird gave up the game and flew away.

G. T. dotted and lined. "One white-throated sparrow."

The crew meandered down the park as the afternoon grew more sullen and they gradully neared the owl tree.

G. T. motioned for silence and the crew stealthily crept forward. G. T. indicated a tree. The crew stared. G. T. nodded his head, and another member of the crew punched the play button on the tape recorder.

The recorded call of a screech owl shrieked in the dusky evening. It was an eerie sound, close to the creature-from-outer-space soundtrack on a 1950s science fiction movie.

Nothing moved in the tree. A dog barked on a ridge back up the trail. G.T. moved on to a turn in the trail for a better look and motioned for a repetition from the tape recorder.

The call sounded again, repeated three times on the tape, perhaps the strangest and most disturbing bird call to be heard in this country.

Nothing emerged from the tree, but an outraged dog charged the crew, followed by its mistress. The dog, unsure of where or what it wanted to attack, paused at the edge of the group. The tape recorder played the call again.

The dog snarled and snapped at the novice, whose life list had been raised to 40 with the addition of the white-throated sparrow, but his face denied the worth of the experience. Susan glared at the beast. G.T. was still intent on the hole and irritably motioning for silence.

The woman muttered platitudes and dragged her dog as it growled.

The disruption faded. The crew joined G.T. and played the owl call again.

Nothing moved in the hollow tree. Binoculars began to waver. One by one they dropped until G.T.'s was the only pair still trained on the hole.

"You don't suppose . . ." he said, stepping forward a few paces into the brush anf toward the tree. "It couldn't be."

G.T. muttered and lowered his binoculars. "You shouldn't do this," he said. "If it is there, I might disturb it. But I have to know."

He swiftly made his way to a hillock a few paces from the tree. He stared directly into the hole until the tension left his body.

He slowly rejoined the group."I think," he said, "that what we thought was an owl is nothing but some odd wood in the back of the hole."

The discussion was short. Both G.T. and Susan had thought they'd seen the owl before. The bird was a wanted resident of that woods. The Hunts had wanted the screech owl to be in that hole, smug, snug and comfortable. But it wasn't.

The crew milled about on the trail. The tape sent the screech through the woods again, but no one looked at the hole in the tree. Rain began to fall. A chill seeped between buttons, through folds.

Red flashed across the ravine. A pair of pileated woodpeckers, lives intertwined against the odds, swooped and played, oblivious to their dull surroundings. Their appearance broke the gloom of the nonexistent screech owl.

"Two pileated woodpeckers," said G.T. and placed his dot and drew his line.

The crew turned and shuffled up another path and made their way toward the Hunt's original pileated woodpecker tree.There G.T. and Susan had seen courtship flight, the drilling of a new nest hole, the early beginngings of a new brood and the first awkward airborne attempts of the young birds. There they had met Shirley Briggs and joined the census.

Like some great ikon, a huge sycamore with several holes in its southern buttress rose to the top of the wood's canopy. By the time the crew reached it the census was completed and the day too dark to see much color on a bird.

The crew took hot coffee and drinks in the Hunt's seventh floor apartment in the middle of the city. The solitary morning dove landed on the window sill and looked into the light. Once the Hunts had fed birds on the sill, but the apartment manager was against it. The dove, silent, walked back and forth.

Susan curled her legs beneath her on the couch and rubbed her cold toes.

"Spring and the breeding season is so much more interesting," she said. "And so much warmer."

G.T., scotch in hand, looked over his clipboard. "We didn't see any bald eagles, did we? Or pink flamingos? People report seeing the strangest birds in that park."

"And no screech owls," said the novice.

"How many birds do you have now," Susan asked him. "Forty. How many do you have?"

"I don't count," she said. "But I have a list."

"G.T.?"

"I don't keep a life list of birds," said G.T. "I keep a life list of life listers."

G.T.'s list includes life listers of birds, life listers of books and life listers of sexual conquests, all of which he finds similar.

The morning dove disappeared into the dark night. The crew settled into the flash of a warm room and whiskey. Susan catalogued the day: 12 species seen, 48 individuals. A slow day, all condsidered, but not discouraging.

Even G.T. was satisfield. "I'll just tell Shirley that the report of a screech owl is not justified," he said. "Whatever else you can say about it, birding is always interesting."

"What did you do with your spare time before you married me?" asked Susan.

G.T. grinned.

"We never went birding together before we were married, did we?" Susan said. "No, I don't think so." She laughed. "Yes, we're quite respectable. Yes, we're quite respectable. Absolutely no premarital birding." CAPTION: Illustration, No caption, By Annie Lunsford