Lunchtime outside the Phillips Collection: The slate-washed sky could go either way -- storm or sun. A sparrow perched high atop one of three massive nests at the corner of Q and 21st streets casts its vote for warmth and light, trilling an insistent song above the nearby Massachusetts Avenue traffic.

At sidewalk level, two white-haired matrons scrutinize the structures, leaning to peer inside a burrow-like opening. A few feet away, three construction workers in hard hats stand shaking their heads, discussing whether the twig-and-branch whirlwinds are alive, or if they fell from the roof.

"I think it must be a kind of topiary," one of the women offers. "How long do you think it took to grow that way?" asks one of the workers. Impressed, he steps back for a good look.

"Mary," the woman's companion cuts in, "you are completely wrong. I'm sure that someone built that thing."

As if on cue, the five turn toward the object of their curiosity, while the bird, undeterred, sings on. Although it's Washington's venerable Embassy Row, the expressions on the line of lifted faces could be drawn straight from the encounter with the monolith in "2001." The scene doesn't surprise Patrick Dougherty, the 47-year-old North Carolina artist responsible for "Chit Chat," the sculpture on the corner, and "Out of Hand," a piece that spirals skyward through the staircase of the Phillips's annex. His installations, along with work by Washingtonian Jim Sanborn and New York artist Meg Webster, make up Part II of "A Dialogue With Nature," the Phillips Collection's ambitious, provocative and unexpectedly successful foray into the murky territory of very contemporary sculpture.

"People don't have to pay admission to talk to you out there," Dougherty says, referring to the eight days he recently spent on the corner installing the piece. "They'll come up and tell you these amazing things -- maybe because we've all had some kind of childhood experience in the woods. Last week a man told me about Big Mr. Twister, a famous tree in his town ... "

"Big Mr. Twister" could describe Dougherty the artist, gathering bundles of sticks from highway mowing sites, the ends of runways, Seattle's forest and Mississippi swamps to fashion primitive structures like nests, like cyclones, like some thing slapped together by Mother Nature to remind the human race that it doesn't hold the franchise on creating shelters or mysteries. An artistic latecomer, Dougherty didn't make his first pieces until 1984, after sitting in on art courses at UNC-Chapel Hill: "Basically, I hung around and watched the artists work, trying to figure out what they did right and wrong."

From the beginning, he worked big. "I wanted to excite people, so I started with these things that wouldn't fit through the door." At the De Cordova Museum in Lincoln, Mass., Dougherty used twisting layers of maple saplings to join the rooftop cupola points to an African-inspired hut.

"Chit Chat," however, is a piece for an urban place. "There's a lot of noise out there {on the corner}, and I had this image that, with those round holes like mouths or ears, {the sculptures} were chitchatting, maybe reverberating like speakers, like a gramophone. Basically," he leans forward conspiratorially, "when people say they can't figure out if it's a bush or something someone put there, then I feel like I'm getting to where I need to go."

Getting where one needs to go is a bit more complicated inside the Phillips, thanks to Dougherty. No more sleek lines for the three-story central staircase -- its polished metal handrail is now hidden by rough branches. A ground-level opening lets visitors stoop and enter to catch a glimpse of ceiling. From this perspective, the tunneled structure seems solid, the ceiling far away. But as one mounts the stairs, the lacy, transparent quality of the branches becomes more obvious. At the top, a twig ledge lets viewers crane their necks like baby birds to look over and down into the light-flecked well. The view is dizzying, yet energizing, as if the spiraling stair journey skyward also has been a mental and emotional progress.

"Pat's piece has energized that space," agrees Linda Johnson, curator of "A Dialogue With Nature" and Dougherty's wife (they eloped in December after meeting through the show). Johnson conceived the exhibition in 1987 as a reaction to the "supermarket-making of art" she believed dominated the art world. Originally, "Dialogue" was to be a full-blown investigation of art inspired by nature. But suddenly it was the twilight of the '80s, money shrank and the Phillips space was deemed too small for the ambitious number of installations Johnson envisioned. "I wanted the impact of a big mass of work," she sighs. (Another Phillips staffer remembers it differently: "People were scared of this show. They were afraid it would shake up our image. Well, it has -- and it's about time.")

To its credit, the Phillips compromised but did not cancel "Dialogue," instead dividing the show into three parts. Carol Hepper, George Lorio and Washington-based Jeff Spaulding opened the series in October with works in which the natural qualities of wood were showcased, the forms still referring to nature in the abstract or overtly (Spaulding's installation relied heavily on discarded Christmas trees). The current phase, on view through June 6, is devoted to organic materials used in site-specific works. Part III will present sculptures by Wade Saunders, Robert Lobe and Suzanne Anker that utilize man-made materials to simulate natural objects.

D.C. native Jim Sanborn's "Coriolis: The Vortex Projection" fills a small gallery across from the stairwell with a meditative work composed around a base-lighted whirlpool; the water's reflection swirls across the shadowed walls like nebulae in space. The piece is based on the fact that whirlpools in the northern and southern hemispheres move in opposite directions, but Sanborn takes it further. The spiraled fossil ammonites scattered across the floor suggest the seabed and the effect of whirlpools. "It's my 'speculative science' about how {the ammonites} got to be the shape they are," he says.

The broken wall levitating diagonally behind the pool is a fossilized ocean bed Sanborn dug up in Utah and reassembled here. It visually and metaphorically links sea and sky, prehistory and contemporary times, while the swirling whirlpool of projected light simulates not only the northern hemisphere's whirlpools, but also the Milky Way.

Like Dougherty's pieces, Sanborn's work pays spectacular tribute to the effects of invisible forces. In contrast, Meg Webster's "Moss Bed" outside the Goh Annex entrance is an understated acknowledgment of nature in the midst of the city.

Webster saw the opportunity to create a piece for the Phillips's august yet intimate surroundings as "a chance to bring the positive aspects of nature into a museum context." She sculpted a low earth mound, covering it with varicolored mosses to make what she contends is her most romantic piece to date, with "bed" connoting love, romance, safety and procreation. "We live in a great garden," Webster says, "and people in cities ignore that."

Washingtonians won't, if these artists have their way. With Dougherty's corner dervishes to draw them in, Webster's bed to lull them, and Sanborn's vortex to set their minds reeling, visitors to the dowager museum of the District may never feel the same about art.

In fact, with "Dialogue," the Phillips itself may have entered a new era of openness to showcasing high-profile, provocative work, an attitude espoused by founder Duncan Phillips but lost over time as the collection became an institution. Certainly the transformation would be a boon for area sculpture lovers who seldom get to see work of this scale and intrigue in either Mall or city museums.