The St. Louis Cardinals swept their second doubleheader in two nights from the Mets at New York, 2-0 and 6-2, last night to build a six-game winning streak and a 3 1/2-game lead in the fast-unraveling race for the NL East Division championship.

David Green's second home run of the season supported a five-hitter by Bob Forsch and Bruce Sutter in the opener, then Darrell Porter had a home run and two runs batted in as the Cardinals gained a half-game on runner-up Philadelphia while shoving Montreal and Pittsburgh 5 1/2 and 6 1/2 games behind, respectively.

Forsch (15-9) went 7 1/3 innings in the first game and led, 1-0, on Green's home run before being relieved by Sutter, who stopped a threat in the eighth inning and recorded his 33rd save.

Pete Falcone (8-10), who shut out the Cardinals last week, allowed only four hits and struck out eight in his eight innings, but Green homered over the bleachers in left-center in the fourth.

In the late game, Jeff Lahti (5-3) relieved starter Jim Kaat after three innings, striking out five and allowing just five hits the rest of the way.

An error by center fielder Mookie Wilson and Mike Ramsey's RBI single gave St. Louis a 2-0 lead in the second inning.