Jim Estes,the 16-year-old from Rockville who reached the semifinals of the Maryland Amateur last weekend, yesterday won his first junior golf tournament this season, the Metropolitan Schoolboy Championship at Germantown Country Club.

Estes defeated Doug Monrow, 3 and 2, in the match-play event.

Estes, who will be a senior at Peary High School in the fall, took home a two-foot-high silver cup engraved with the names of the 47 previous winners of the oldest junior tournament in the country.

His victory culminated four days of qualifying and elimination rounds. The tournament started Monday at Marlboro Country Club with 135 high school boys from metropolitan Washington competing.

In the 14-15-year-old championship at Kenwood Wednesday, Peter Nadayani of Langley defeated Jim Hecht of Madison in 23 holes. Fifty-five players entered that tournament.

Estes reached the 16-17 final by beating Annandale's Dave Newland on Greencastle's 20th hole Wednesday. Monroe defeated Bowie's Pat Staveley on the 19th hole in his semifinal round.

Estes led throughout the final match, closing it out on the par-4 16th hole. But after sinking an eagle-3 putt on the par-5, 570-yard 14th hole, Estes had faltered on No. 15.

Both he and Monroe drove into a high-grass hazard on No. 15. Then, Estes hit into a second hazard and Monroe won the hole, narrowing Estes' lead to 2 up.

"I thought on the 15th I was going to give the game back to Doug," Estes said. "He could have gone on to win it from there."

Monroe, a senior-to-be at Whitman, didn't win a hole until the par-5 No. 7, where he sank an eight-foot birdie putt. He birdied again to win the 11th hole, won the 13th with par, then took the troubling 15th.

Estes parred the first three holes and was 4 up after 10 holes. Monroe never got closer than 2 down after the first two holes.

"Neither of us played as well as we could have today," said Monroe, 17, who has been a good friend of Estes on the junior golf circuit the last three years.

Estes, who finished third in the Maryland high school championships in October, came into the Schoolboy tournament having won three tournaments last summer, including the Maryland Junior and the Tournament of Junior Champions.

Monroe, who never has won a junior tournament, was twice a runner-up in junior events last summer.

In the Schoolboy's early rounds, Estes defeated Cobby Webb of Paint Branch, 9 and 8, and Mark Bureau of St. Stephen's, 2 and 1, en route to meeting Newland in the semifinals.