Keith Moreland had a double and single during a seven-run sixth inning yesterday in Chicago and Dick Ruthven yielded only four singles to lead the Cubs to an 8-0 rout of the Montreal Expos.

The loss knocked the Expos out of first place in the National League East Division, a half-game behind Philadelphia, which beat New York, 2-1. Pittsburgh, which beat St. Louis, 7-5, is 1 1/2 games back; St. Louis trails the Phillies by two games.

Montreal starter Steve Rogers (17-10) lost at Wrigley Field for the first time since Aug. 3, 1980 as he gave up 10 hits in 5 1/3 innings. Ruthven (12-11) picked up his fourth complete game and second shutout.

Ruthven scored the first run of the game in the third inning after leading off with a single. Dan Rohn reached base on a sacrifice attempt as Rogers' throw failed to get Ruthven at second. Bill Buckner singled to fill the bases and Ruthven scored when Moreland's grounder was fumbled by third baseman Tim Wallach for an error.

Moreland led off the sixth with a double and scored on Ron Cey's double. Carmelo Martinez singled Cey to third and Jody Davis doubled in pinch runner Jerry Morales, with Martinez being cut down at the plate. Larry Bowa then singled Davis to third and Davis scored when Wallach fumbled Ruthven's grounder, making the score 4-0.

Dan Schatzeder gave up a two-run single to pinch hitter Ryne Sandberg, who took second on the throw to the plate and scored the sixth run of the inning on Buckner's double to right. Moreland then got his second hit of the inning, a single to left to score Buckner.

"I got myself into all kinds of trouble, particularly on the ground balls," said Rogers.

Rogers said ground balls in the sixth inning by Moreland and Cey proved decisive.

"Hard-hit ground balls at Wrigley Field almost always will turn into hits," said Rogers. "I have always psyched myself up for the Cubs because they have been such a good hitting club. But today, I think I overdid it."