A piece of advice from his Bethesda Country Club pro has paid off for Doug Monroe, the Whitman High School senior who has assaulted Woodmont's South course for 10 birdies and an eagle in three rounds of the Bobby Gorin Memorial junior golf tournament.

Pro Jim Folks advised Monroe to hit his irons with an easier, three-quarter swing and the 16-year-old responded by playing one-under-par golf in two matches yesterday. Monroe defeated James Brown of Brooke Manor, 3 and 2, and Paul Hiskey of Washington Golf and Country Club, 3 and 1.

In this mnorning's semifinals, Monroe will play medalist Keith Abbott of Lakewood at 8 o'clock, followed by Jim Estes of Manor versus Mike Reese of Congressional.

Monroe eagled the seventh hole and shot a front-nine 31 to take a four-hole lead over Brown.

Metro schoolboy champ Estes also went on a birdie binge. Estes bombed Ed Molloy of Crofton, 5 and 4, in the morning and then assumed a three-hole lead over Ken McDonell of Ft. Belvoir by opening with birdie, par, eagle. McDonnell fought back to take a 1-up lead after nine but Estes birdied 11, 12, 15 and 16 for the victory.

Abbott saw Tom Splaine of Montgomery Village self-destruct with two back- nine double bogeys before scoring a 4-and-2 victory.

Reese had a fairly easy time of it. He cruised past Blaine Coblentz of Wheaton in the morning, 4 and 3, and then blitzed Chris Rouse of Fort Meade, 7 and 6.