Now Nelson Burton Jr. may find out why the bowlers he so often analyzes on television perform as they do.

Burton spends most Saturdays as the color commentator for ABC's telecasts of the Professional Bowlers Association tour. He will spend his big moments today trying to win the $11,000 first prize in the $90,000 PBA Fair Lanes Open at Fair Lanes-University in Adelphi. Actually, he sees the assignment as much easier than trying to tell viewers why one of his colleagues won or lost.

"I've never been able to give anybody an excuse," said Burton, who ended the match-play competition last night in first place.

"Now I might find out why someone wins or loses. It'll be a good experience for me, particularly from the television standpoint moreso than from the bowling itself. I'd certainly rather be bowling than watching, though."

He will be bowling just one game because he strung lines of 236, 193, 268, 290, 211, 203 and 238 to climb from third after 34 games earlier in the competition to first. That will afford him the luxury of watching while Mike Aulby, Matt Surina, Steve Hiscox and Teata Semiz, who finished second through fifth, try to eliminate each other in order to eliminate Burton. Burton's only defeat last night occurred when Aulby, last year's rookie of the year who climbed from 115th after six games here, beat him, 209-185, in the position round.

"I've been real steady all week," Burton said. "The only time I really moved away from anyone was in my third and fourth games, when the guys behind me had marginal games. It's great to be first, because I've got a lot less work to do to win. But the tournament leader has lost eight times in a row, for reasons that nobody can figure out. So there's some pressure there. I also won't throw a ball for about an hour and 10 minutes, while the other guys will have already bowled at least one game. Then all I get is three practice balls."

If he continues his current form, he can give them to the opposition. He was the only member of the top five not to lost a game last night. Aulby, who was second after 34 games, dropped two. Surina fell from first to third during the final eight-game block, while Jeff Mattinly, fourth after 34 games, missed qualifying for the finals by eight pins after losing, 219-168, to Surina in the position round.

Mattingly's failure enabled Hiscox, a 23-year-old rookie from Tuscon who has not cashed a check in his nine-tournament career, to edge into the fifth spot. Hiscox was 14th after 34 games, and entered the position round 65 pins behind Mattingly, 27 behind Semiz and 14 behind sixth-place Dave Beckmann. But there was just enough room for him to qualify with a 223-201 victory over George Pappas.

"I think I'm in pretty good position," acknowledged Aulby, after covering the most ground to arrive in the top five. "I've only got to bowl two games, and I'm guaranteed third place money ($5,000). I threw real well after the first day, and it always gives me a kick to be the only left-hander out here.

"I had two bad games tonight, then threw only one or two bad balls until the last one. (He left a 4-6-7-10). I was thinking about locking out Surina. I don't usually watch the scoreboard, but I was on that one. I should have kept my eyes on the alley."