Marty West of Columbia County Club coasted to his third Middle Atlantic amateur championship at Washington Golf and Country Club yesterday, piling up a nine-stroke lead over his nearest pursuer.

This was the largest margin in the history of this tournament, which goes back to 1902.

West shot 73 yesterday for a 72-hole total of 282, two over par but nine better than Paul Erhardt, the defending champion and 10 better than Steve Fellinger the University of Maryland left-hander.

Henri de Lozier of Columbia Country Club, like West a player of national quality, shot 72. In this tournament there were only three subpar rounds and one par round.

The Mason-Dixon team that will face Philadelphia at Chevy Chase next weekend was named: West, de Lozier, Jim Millar, Ben Brundred, Henry Blue, Perky Cullinane, Bill Sibbick, Pete Van Pelt, Dave King, Butch Mielke and seniors Bob Morris and Ralph Bogart.

West played with his two nearest pursuers, Erhardt and Fellinger. West started the day with a four-stroke lead over Fellinger and increased it to six when he birdied the first hole. By the 15th hole, all element of contest was gone as West had increased his lead to 10 shots.

He had three birdies and three bogeys on the front to go out in 35, and one double bogey, three bogeys and two birdies on the back for a 38. Erhardt had a closing round of 75, and Fellinger 79.

"I was ready to play if they charged me," West said. "But it was just one of those days that I had no real opposition."

West has won nine major area tournaments.