It is understandable that when Bill Rigney, the manager of the California Angels, speaks of Relief Pitcher Minnie Rojas he does so in superlatives. Rigney claims that Rojas "has been just about perfect" and says unabashedly that in his 12 years as a manager, "I've never had a reliever who could throw strikes better." A month ago the Angels were in last place and about all that Rigney had going for him was a tenuous vote of confidence from a disenchanted front office. Last year the Angels finished a promising sixth and, hoping to move up even higher in the standings, traded Dean Chance to the Twins for Don Mincher and Jimmie Hall. Chance became the early pitching sensation of the league, and not even a flurry of homers by Mincher could placate Angel fans. Barely 14,000 showed up for a "big" double-header against the Orioles. That might have been a blessing, for the last place Angels lost 16-4 and 11-1. Then, as if borrowing some magic from nearby Disneyland, the Angels began winning. They won 19 of their next 26 games, reached .500 and were only 2� games out of second place. No one contributed more during this upward climb than Minnie Rojas. He was called on to relieve 14 times, gave up 11 hits in 26? innings, had an ERA of 0.31, won four games and saved eight others. These accomplishments have been gratifying for Minervino Alejandro Rojas, who at 20 was a soldier in the Cuban army, at 26 was toiling in the Mexican League and now, at 28, is the most effective reliever in baseball. Although soft-spoken Minnie says little, Rigney, still gainfully employed, is always ready to serve as his spokesman.