Paul McGowan was in an envious position for Soap Box Derby enthusiasts. His daughter Martha, 14, and his son Peter, 12, were pitted against each other in a final Saturday of the 1982 Metropolitan Soap Box Derby.

"I guess you could say this is the ultimate," said McGowan, a Rockville resident who heads a District architectural firm. "I've been involved in soap box derbies since 1950 when I built cars for my brothers. But this hasn't happened in my family before."

The derby, sponsored by the Greater Washington Soap Box Derby Association and the Downtown Jaycees, attracted 30 drivers vying for two spots in the All-American Soap Box Derby on Aug. 14 in Akron, Ohio. Forty-two drivers competed last year.

When a driver lost, he was placed in the losers' bracket, where another loss resulted in elimination. The winner of the losers' bracket raced the undefeated survivor of the winners bracket for the championship.

Martha McGowan, a racer for four years, lost her first race Saturday but won every race in the losers' bracket. Because her brother, Peter, who has been racing for three years, advanced to the finals of the winners bracket, Martha would have to beat him twice to win the senior division, ages 12 to 15.

"I'm going to whoop your seat," Martha warned Peter. "You may be bad, but you're not that bad," retorted Peter.

Martha won the first race on the 953 1/2-foot course along Eastern Avenue NE, near Varnum Street, but lost by a hundredth of a second in the second race. Peter's winning time was 30.22.

In the junior division, ages 10 to 12, Jonathan Tivel, 12, of McLean, in his third year of derby racing, defeated Danny Bublitz, 10, of Arlington. He and Peter McGowan are now preparing their racers for Akron.

The drivers built the cars, made of wood or fiberglass, under strict specifications and limited guidance from adults.

Junior division cars are 80 inches long, 13 inches high and 14 inches wide and cannot weigh, with driver, more than 220 pounds. Senior division cars are 84 inches long and either 13 inches high and 13 inches wide or 12 inches high and 14 inches wide. The car is limited, with driver, to 250 pounds. Lead weights are added to bring cars up to the maximum weight.