Left-hander Mike McCarthy of Silver Spring played solid golf for the necessary 33 holes to score a 5 and 3 victory over Barry McCarty of Alexandria and win the 73rd Washington Metropolitan Golf Association Men's Amateur yesterday at Montgomery Country Club.

It was the biggest win for McCarthy, 32, a steady player who has won the Argyle club championship two of the seven years he has been a member. He teamed with Stu Strang to be runner-up in last year's Belle Haven Four Ball and in 1978 reached the quarterfinals of the Maryland Amateur.

McCarty, eight-time Belle Haven club champion, shot the opening nine in 2-under-par for a 2-up lead on McCarthy, but McCarthy then won three straight holes to take the lead for good.

"That was sort of the key," said McCarthy. "If he had gotten a little more up it might have been a different story. I hit the ball real well, real solid all day."

McCarthy finished the morning round 2-up after McCarty, who won this tournament in 1980 when it was called the District Amateur, three-putted the 18th hole.

McCarthy assumed command by winning three of the first five holes of the afternoon round. McCarty lost the first hole by three-putting for bogey in pouring rain. On the next hole, the rain subsided but not McCarty's problems as he drove under a tree and took bogey to lose the second hole and fall 4-down.

On the par-4 fifth hole, McCarthy hit two big shots and holed a 20-foot birdie putt to send McCarty 5-down.

It appeared McCarty might win the par-4 seventh hole in the afternoon after McCarthy drove behind a tree but McCarthy somehow avoided the trees and hit his second shot onto the green, then sank a 15-foot birdie putt that matched McCarty's chip-in birdie.

"I thought I was coming back," said McCarty, 32. "When I chipped in for birdie, he made a birdie on top of it. It really demoralized me. Mike hit the ball very well. I had the feeling he wasn't going to let me in the match. He was relentless."

On the par-5 13th hole (the 31st of the match) McCarty hit a pitch shot that hit the flagstick and stopped two feet away for a birdie to pull him within four. The match ended at the par-4 15th hole, where McCarty bogeyed and McCarthy sank an eight-foot par putt.

The two had played each other in high school and college , McCarthy attending Good Counsel and James Madison, and McCarty playing for Ireton and Virginia Tech.