A young golfer whose main claim to fame had been that he was "Lanny's brother," came to the 72d hole of the $200,000 Tucson Open today tied for first place with last season's player of the year.

Form, and experience prevailed.

Bobby Wadkins, the 26-year-old from Richmond, whose best previous finish in four years on the tour was eight despite once leading after three rounds, bogeyed the final hole. Tom Watson, playing a threesome behind, parred the 18th for a par-72 round and a four-day total of 276, 12 under par.

"I honestly didn't know who I stood, coming to the 18th," Wadkins admitted. "I'd seen the leader board at 17 and I still thought Watson was 13 under, a stroke ahead of me. So I told myself I still had one big shot to hit, and I thought I did, but the nine-iron I skipped up there from off the front fringe went about 10 feet past and I just didn't make it coming back."

Wadkins wound up with a 71. He earned $22,800, which was more than his previous four-year total.

Watson, playing in the final group, saw Wadkins' troubles on 18. The 1977 Masters and British Open champion, given the opportunity to earn $40,000 with a par, methodically wrapped up the tittle. He was fortunate, however to have held onto the lead through the last six holes.

"I was lucky not to have been hurt on 13," Watson acknowledged. "I pull-hooked my tee shot but the ball found an opening, near a swail, and I was able to a clear approach to the green. Then, at 15, I hooked into a tree, and 16 I faded into a bunker."

Watson won this tournament with his superior play the first two days, posting rounds of 63 and 68. He played well early this afternoon, going one-under with an eight-inch tap-in birdie on the sixth green. And his iron play over the next six holes was excellent, giving him birdie opportunities from six to 12 feet.

"I could never set it going with my putter through that stretch, when I could have put the tournament away," Watson said. "My failure to score there was what made things so close at the end."

Bill Rogers, Jerry McGee and Lee Trevino all challenged, coming within a stroke or two of the winner during the earlier stages of the final round. They all came up short, however, enabling the late-closing Howard Twitty to take third place at 270, two strokes back. Charles Coody and Keith Fergus tied Trevino for fourth, one shot behind Twitty, whose 68 today was helped when he chipped in for a final-hole birdie.

The closest Watson came to having the lead taken from him this seek was today when Wadkins was on the 17th green. The former Virginia state amateur champion was 30 feet from the cup, Watson was just about to bogey 16 and Wadkins struck what appeared to be an excellent putt.

The ball hung on the back lip.

Still it was a surprising effort, overall, by Wadkins. He was carrying the family banner here after his older brother, PGA champ Lanny, had failed by two shots to qualify for the final two rounds.

Watson emerged from this tournament as "the one to beat" wherever he plays in the Far West the next month. He captured the Crosby at Pebble Beach and the San Diego Open last january.

The Stanford graduate did, however, leave a little to be desired this week as a prognosticator. He thought 20 under par would be required to take the Tucson, following his hot early start in the desert.

Watson's 276 was one stroke more than Bruce Lietzke's winning score last year. It was far off the record 263 fahioned here in 1975 by Johnny Miller.

Miller shot 297 this time around, Lietzke 286.