Around the bars during spring training, the reporters and expert fans who go to Florida to watch the teams shape up agreed almost unanimously on one thing: Detroit's Denny McLain would be lucky to win, say, 16 games this year. McLain had won 31 in 1968, but the logical evidence against anything approaching that figure seemed obvious. Denny pitched a grueling 336 innings last season and then came up with a sore arm for the World Series. In the winter there had been no time for rest between his nightclub appearances as an organist and his flying lessons. Besides, the argument went, he had won many of his games because his team scored more for him than for any other pitcher. Four times last year McLain was pulled from games only to win them in the clubhouse as his team pushed over the go-ahead run in the inning in which he left. The Tigers have not hit nearly as strongly for their 25-year-old ace this year but, by last week, McLain had struck out all the logicians. With a 3-1, seven-hit victory over the Angels, he became the year's first 20-game winner (20-6) and solidly established himself as baseball's toughest pitcher. "I had to win 20 this year to prove last season was no fluke," he said. McLain has an outside chance at another 30-victory season if he chooses to try for it. Manager Mayo Smith figures Denny has just nine starts left, but the pitcher disagrees. "Hmm, there are 5� weeks left," he said. "That means I could make about 14 more starts. No, sir, I'm not interested in 14 more starts. My pitching arm's not sore, just tired, very tired." Now, that is logical for a weary man who has had no rest in 18 months and has already pitched 261 innings this year.