Bill McGuinness, a slight 17-year-old from Woodbury, N.J., who is headed for Notre Dame in the fall, won the ninth annual South Atlantic Junior golf championship at Crofton yesterday, 1 up, over Richard Montefusco of Westwood.

After McGuinness had par to Montefusco's birdie on the 17th, Montefusco came within an inch of winning the 18th but his 25-foot putt for a birdie hung on the lip.

Dave Nocar of Chartwell took the 14-15 division, 6 and 5, over Webb Heintzelman of Washingtonian.

The two finalists in the 16-17 class survived a grueling marathon that started Monday with an 18-hole qualifying test and two matches a day Tuesday, Wednesday and yesterday.

In yesterday's morning matches, McGuinness defeated Dick Getek of Richmond, 1 up. McGuinness never led until the final hole, Getek three-putting to lose the match to par. Montefusco ousted Bob Wren of Richmond, 3 and 1, sinking a 20-footer on the 17th.

The final was a test between fine young golfers, determined and never yielding. The two were never separated by more than one stroke. Montefusco won the second hole with a birdie from fice feet but he three-putted the sixth to lose to par. Montefusco again took a 1-up advantage with a par four on the seventh.

McGuinness won the ninth and 10th with pars to go ahead for the first time. But Montefusco birdied the short 12th from three feet to again square it. McGuinness won the 15th, coming out of the woods with a brilliant second shot and sinking a six-fotter for a birdie.

Again Montefusco evened it with a birdie at the 16th.

On the short 17th, Montefusco's tee shot carried over the green and his opponent reached safely. Montefusco chipped over the green and took a bogey to McGuinness's par to fall one behind.

Both were on the green in two on the 18th. McGuinness was away and put his approach putt a foot from the hole. Montefusco's ball didn't have the steam to make the extra turn and that was it.

McGuinness had a two-over-par 74 and Monterfusco 75.