About a thousand people sat flinching around the West Potomac Park Polo Field yesterday as about a hundred others tossed boomerangs at them and the boomerangs properly curled away and back to the persons throwing them.

It was the fifth annual Now You See It - Now You Don't - Now You See It Again Smithsonian Boomerang Tournament, featuring boomerangs, some leaving trials of smoke because they had smoke bombs attached to them, others with four wings instead of the normal two.

Participants caught boomerangs with their feet, behind their backs and one threw a boomerang that came back and knocked a fake apple off his head.

"Boomerangs are the thinking man's Frisbee," said Benjamin Ruhe, director of the stunt show and competition.

"There is a lot of interest in individual sports," he added, "not the team sports, and here is a sport where you play catch with yourself. Plus, there is a lot of interest in the Stone Age and Stone Age culture and this is a Stone Age device."

The boomerange show and competition drew a large crowd that even surprised some of the people who found themselves in the crowd.

"Boomerangs?" said Edward Phillips of Arlington. "I don't know why I've been sitting here for an hour watching them throw boomerangs, so I'm not going to try to tell you."

"It's fun to watch," said Bob Heffernan of Washington. "It's fun to see people go out and try all kinds of weird crazy things like catching it with their feet."

Several persons in the crowd said they learned about boomerangs by taking a seminar taught by Ruhe, who directed yesterday's competition for the Smithsonian. Ruhe said he learned about the boomerang in Australia shortly after he finished college in the late 1940s. He was a jackeroo, a cowboy, on a farm in Australia. Later he wrote a book on boomeranging called "Many Happy Returns."

"I didn't use the boomerang on the farm in Australia for anything serious," said Ruhe, after he explained that it could be usd for hunting and warfare. "I was just taken with it when I saw it and I've been learning about it ever since."

Joe Dougherty, of McLean, who entered several of the boomerang competitions, including throwing two boomerangs at once and catching them both, said he made a quick exit from his graduation ceremony at McLean High School to take part in yesterday's competition.

"I get more interesting look than weird looks when I practice in McLean," said Dougherty. "People appreciate the skill involved if they watch you. You see it's more skill than strength, really. It is only a matter of strength in the distance throws."

Dougherty, who said he has been throwing boomerangs for six years, said the sport "releases nervous tension" for him.

James McGraw, of Washington, another contestant, said he finds boomerang throwing mentally challenging because the boomerang operates on aerodynamic principles.

"I became interested in throwing the boomerang while I was taking physics in high school," he said as he waved around his favorite boomerang, one he made himself. "The boomerang displays all the principles of flight."

Yesterday's competition featured an attempt to set a world record by throwing 13 boomerangs in the air before the first boomerang that was thrown landed.

Allan Woolly, of Wheaton, got 10 of his 13 boomerangs into the air on his first attempt before the boomerangs started landing. On his second attempt he got only eight off, again failing to break the world record.

In addition to local boomerangers there were several experts from around the world at yesterday's tournament. Herb Smith of Sussex, England, the long-distance world record holder, was there, and so was Max Hoeben, Holland's leading expert on the sport.

"I've been coming out to see this thing for a few years now," said William Rust of Washington. "I just get a kick out of watching it come back: I even bought a boomerang but I keep it in the closet the rest of the year."