Mets righthander John Maine, who had the lowest ERA in the major leagues in April, on Wednesday was named National League Pitcher of the Month. The 25-year-old Maine led the majors with a 1.35 ERA and posted a 4-0 record. He allowed just five earned runs in 33 1/3 innings, never surrendering more than two runs in any start. Acquired from Baltimore in the Kris Benson deal prior to last season, Maine held opponents to a .159 batting average and recorded 30 strikeouts for the Mets, who have won each of his starts.