ST. LOUIS, SEPT. 30 -- If the Cardinals want to avoid facing the New York Mets pitching staff with something on the line, St. Louis' favorite team has to figure out a way to score some runs.

Never has a 3 1/2-game lead with four to play looked as precarious as after tonight's 6-1 loss to the Montreal Expos that deprived a Busch Stadium crowd of 45,829 of a National League East division-clinching victory.

Pascual Perez struck out six Cardinals and walked none over seven innings, yielding only four hits and an unearned run in posting his seventh win against no losses since coming up in midseason. The Expos are now 9-0 in Perez's starts, 11-0 in games he has appeared in, and remain a game away from pennant elimination.

Bob Forsch (11-7) took the loss as St. Louis managed but five hits against three pitchers. In the three games played in this four-game series, the Cardinals have scored five runs on 12 hits.

Nevertheless, St. Louis can do no worse than tie for the NL East title, thanks to the Mets' 4-3 loss in Philadelphia. Even if the Cardinals lose Thursday to the Expos, they would only need to win one of the three concluding weekend games with the Mets to clinch their third title in six years.

"I know when we've lost two in a row or three in a row, it's my turn to pitch," said Perez, who has won all seven games in September to set a club record while posting an ERA of 2.28. "We've got four more games left. You never know what can happen."

What must happen if St. Louis is to hang on is simple: the Cardinals have to get some run production. In its last eight meetings with the Expos, St. Louis has averaged just more than two runs per game.

"We might explode for three or four runs, you never know," said No. 3 hitter Tommy Herr half-convincingly.

"It's no surprise that we haven't hit the ball against Montreal because they've shut us down all year."

Tonight, Perez kept the Cardinals off step with a tough slider, then put them away with a deadly inside fastball. Getting the inside strikes from home plate umpire Lee Weyer made Perez an imposing figure on the mound.

Perez has now thrown three complete-game victories in his last five starts. Since his recall from Class AAA Indianapolis Aug. 19, the worst he's done is a five-inning stint in his first game.

Tonight, he reverted to some of the antics that brought him disfavor while he was in Atlanta, such as faking a throw between his legs with Vince Coleman on first base in the fourth inning. The crowd booed heartily, but Perez was unshaken.

"In Montreal, the people like me a lot," he said. "Here, I heard the boos from the people because I did some damage."

The Expos nicked Forsch for a run in the second on singles by Tim Wallach and Tom Foley and a sacrifice fly by Herm Winningham. St. Louis manufactured its run in the fourth. Coleman singled, went to second on Ozzie Smith's single and took third when Perez's pickoff attempt went off shortstop Hubie Brooks' glove into center. Coleman scored on Herr's grounder to second.

Montreal broke back on top in the sixth. Tim Raines singled but was forced by Mitch Webster. Brooks followed with a shot to center that Willie McGee could only get a glove on, Webster stopping at third. Wallach was walked intentionally, then Andres Galarraga hit a high chopper to Terry Pendleton. The third baseman looked toward home, then toward first, but had no play anywhere, and Webster scored.

Ricky Horton relieved Forsch and gave up a grounder by pinch hitter Dave Engle that scored Brooks and put the Expos up by 3-1.

"It's been great. It's been fun," said Brooks, whose ninth-inning triple to right center scored three to clinch it.

The Expos would have been even more important if the Cardinals had not somehow managed to sweep a doubleheader Tuesday night while scoring four runs on seven hits in two games.

"That's how important {Tuesday} was," Brooks said. "That's why we were emotionally shocked . . . I had to get myself going."

"When I see my team lose two games, two shutouts," Perez said, "I didn't sleep last night. I'd give my heart to this team right now."

Andy McGaffigan and Tim Burke came on for Perez, though he said he felt fine, and between them gave up just one more hit. But that's nothing new for the Cardinals.

They have a great chance tonight, sending Danny Cox against Jay Tibbs, who has spent most of the season with Indianapolis, posting a record of 5-5 there with a 2.99 ERA. In the NL this season, Tibbs is 4-4.

Even without injured slugger Jack Clark, St. Louis has played .600 baseball (12-8) and extended its stay on top in the NL East to 133 days.

"They go into a tailspin offensively and can still score two or three runs per game," Brooks said. "And if they use their bullpen they have a chance to win ball games."

But they'll have to put the bubbly back on ice, at least until Thursday. "I guess the champagne has to wait for awhile," Brooks said. " 'Cause I know they've got it over there."