For the 640 children of Arlington's Abingdon Elementary School, the man in the red T-shirt with the long gray hair and handlebar mustache was Santa Claus come early.

"I'd like a castle with a dungeon, a bridge and tunnels," said one of a crowd of second-graders clustered around a cafeteria table with Robert S. Leathers, the Pied Piper of America's playgrounds. "I want a tree house with a swing and slides" . . . "an alligator" . . . "a dragon" . . . "a maze" . . . "a water slide and a roller coaster," chimed others.

"Well, I don't know about the water slide and roller coaster," said Leathers, whose arrival at Abingdon was heralded with school banners, songs written in his honor and classrooms filled with pictures of playgrounds.

Leathers, from Ithaca, N.Y., not the North Pole, was back in Northern Virginia recently to preside over the design and construction of eight more of his giant wooden "creative play areas."

That brings to about 50 the number of Leathers playgrounds in Northern Virginia, valued at as much as $100,000 each and built by more than 25,000 suburban volunteers. In addition, thousands of children helped Leathers design the playgrounds.

"He's a genius, a playground artist," said Penny Wald, the volunteer who coordinated construction last spring of the Beverley Hills Cooperative Preschool in Alexandria.

"He not only got kids to help design the playground," Wald said, "but he got more than 100 people who'd never built anything in their lives cooperating . . . everybody working, friendly, productive. I've done a lot of things, but this is probably the most exciting, exhausting thing I've ever done in my life."

Leathers, an architect of custom homes who builds playgrounds as a hobby, was back home in Ithaca Monday "in a semicomatose daze" after his two latest Washington-area whirlwind visits. During the two four-day visits, timber playgrounds were constructed by volunteers at five schools and a synagogue -- in Reston, Warrenton, Falls Church, Vienna and Arlington -- and three other playgrounds were designed -- in Vienna, Alexandria and Arlington -- and will be built next spring.

Although he has designed more than 200 timber playgrounds, including many in California, Texas, Colorado and Iowa, there are more Leathers playgrounds in Northern Virginia than in any other single place. He has done none in Maryland or the District "for humans," he said. However, he recently designed the new wooden playground for the National Zoo pandas, Ling-Ling and Hsing-Hsing.

The zoo playground in the District is the only Leathers playground not built by local residents. But then, he notes, pandas are notoriously lazy.

While half of the playgrounds built in the United States are now made of wood, according to New York playground architect M. Paul Friedberg, few are built by volunteers.

"I don't know Leathers . . . but I think it's wonderful when a professional helps a community to build things. It sure sounds like a labor of love . . . . It certainly doesn't sound like he's making a big profit out of it," said Friedberg.

Leathers said his fees have ranged from $1,800 to $5,500, including a design day visit, constant consultation on organizing and buying supplies and then overseeing by Leathers or his staff of the actual construction, which takes four days. Transportation and lodging for Leathers and assistants are extra, but then they usually stay in the homes of volunteers.

While the shapes of the playgrounds differ, the materials are all simple and similar: telephone poles sunk in the ground with a superstructure of large splinter-resistant wood (No. 1 grade southern pine) treated with a nontoxic preservative that should make the playground last at least 30 or 40 years, Leathers said. Old varnished tires are used for swings and coated cables support bridges.

At Arlington's McKinley Elementary School, a playground built by volunteers two weekends ago cost about $19,000, although the school PTA estimated it would have cost $75,000 to do what parents, friends and students did in four days and nights, working under floodlights provided by the county fire department.

McKinley seventh-graders Jason Watkins and Zachary Jocelyn, both 12, raised money for their playground and helped build it as well. "We got $500 by knocking on about 200 doors. One person gave us three cents, but then another made up for it and gave us $30. We almost fainted," Watkins said.

The food for all playground volunteers is usually donated, as are many tools and supplies. The Virginia Electric Power Co. and C&P Telephone Co. frequently donate the utility poles and crews to dig post holes for the playgrounds.

Not all of Leathers playgrounds involve schools with 600 pupils and work crews of more than 100 parents as the Abingdon one did. A Leathers playground on Cranberry Island, Maine, "was for a kindergarten to eighth-grade school with seven pupils in it," Leathers said. "The kids there wanted seven of everything, seven swings, seven slides, seven tunnels, and a tower so they could see all the other islands."

Building the Cranberry Island playground reminded Leathers of his first playground 14 years ago, which was for his own children's school in Ithaca.

"It was a barren playground with one basketball backboard and our PTA only had $1,500." That's when he volunteered to design one from recycled materials, like old tires and wood, as was done with the "adventure playgrounds" of Europe made by children out of postwar rubble. Other schools soon asked if Leathers would do the same for them, with new wood, and his hobby began taking more and more of his time.

Modern wood playgrounds began to be built in this country in the 1960s and are a fantastic improvement over their barren jungle gym predecessors, said Friedberg, who has built close to 200 playgrounds and written two books on the subject.

"But while I don't know Leathers' playgrounds, I suspect his and mine, while more creative than the old playgrounds, still are too sanitized . . . and lack the vital, messy, changing environment" that children seem to love.