The hitting of Keith Hernandez, Willie McGee and George Hendrick enabled the St. Louis Cardinals to sweep a twinighter in New York last night and increase their lead over their two closest competitors in the NL East.

McGee's looping 10th-inning double drove in Hernandez to win the opener against the Mets, 3-2. In the second game, Hernandez drove in the go-ahead run in a 7-1 victory.

The Philadelphia Phillies fell three game behind by losing to the Pittsburgh Pirates, 4-2, and the Montreal Expos fell four back by losing to the Chicago Cubs, 3-1.

Manager Whitey Herzog of the Cardinals noted the help of the Pirates and Cubs.

"We need all the help we can get," he said. "We came into Shea Stadium worried about playing two doubleheaders back-to-back and a single game on Sunday. But Eric Rasmussen pitched a fine game and Steve Mura wasn't too far behind."

Bruce Sutter, working in relief of Rasmussen, was the winner in the opener. Mura (12-10) was credited with the victory in the second game with the help of Doug Bair, who earned his seventh save.

"My pitching has been good this year," Herzog said. "I have no complaints. But this race is far from over. A three-game lead is great if you have only two games left. And don't forget, we have two games against Philadelphia, two against Montreal and four with Pittsburgh. Plenty can happen."

The Cardinals broke the second game open with three runs in the eighth off relievers Mike Scott and Carlos Diaz. McGee drove in two runs with a bases-loaded single and Ken Oberkfell doubled in another.

In the opener, Hernandez opened the 10th by walking against reliever Neil Allen (3-7) and moved to second as Hendrick beat out an infield hit. One out later, McGee, who had been hitless his last 24 official at bats, dropped a soft fly ball beyond the reach of diving center fielder Wilson, allowing Hernandez to score.

Dave Kingman of the Mets, the league's home run leader, hit his 37th in the opener.