Alexandria's annual Scottish Games was marred by its first accident yesterday when the event's athletic director was struck by a caber, a 140-pound, 20-foot tree trunk, being tossed by a competitor.

Witnessess said David McKenzie, 42, a D.C. police officer, was standing with his back to the competitors, trying to ensure that the playing field was clear of spectators when the accident occurred, shortly before 2 p.m..

He was taken to Alexandria Hospital, treated for separation of his right shoulder and released. Dr. Richard Price said the injury should take three to six weeks to heal.

Bill Quay, one of the founders of the Virginia Scottish Games, said the caber toss is probably the most dangerous of the seven events included in a competition called the Highland Heptathlon.

"It is dangerous for the spectator because of this type of accident," said Quay.

Yesterday's mishap was the first accident in the 13 years the event has been held in Northern Virginia, he said.

Spectators are cautioned to remain behind rope barriers during the toss, which was described in publicity sheets as "the event with the greatest crowd."

"The athlete tosses a 140-pound, 20-foot tree truck so that it somersaults in midair and lands exactly parallel to the athlete. This is a test of skill, agility and strength."

The accident came on the opening day of an event that drew an estimated 25,000 people to the Episcopal High School grounds at 3900 W. Braddock Rd. The games will end today.

The school grounds were filled with the sound of bagpipes and Celtic harps yesterday as about 70 clan associations were represented at the festival, offering literature about their clans and souvenirs from Scotland.

"Most Americans are interested in their roots and background," said Quay. "Many people come to look into their ancestry."

Alexandria's games are among the largest in the nation, drawing spectators and participants from as far away as California and Canada. The winner of the heptathlon is given a $1,000 award toward a trip to Scotland for competition in the Highland Games.

Today's highlights include the British Car Show, more games and the U.S. National Scottish Harp Competition.

Competitors from throughout the United States will vie for a trip to Scotland to study the ancient instrument.