In the Montreal Expos' dressing room, broadcaster Duke Snider was trying to spread some cheer, reminding the players that his 1962 Los Angeles Dodgers had led by four games with six to go and wound up losers in a playoff with San Francisco.

In the Philadelphia Phillies' clubhouse, Manager Paul Owens was saying things like, "There are nine games to go. We still have to go out and battle. It's not over yet."

Except for exercises in history and mathematics, however, it would appear that the Phillies' doubleheader sweep of the Expos before 47,364 chilled fans has forced baseball's most notable "wait till next year" club to do just that once again.

Pounding out 9-7 and 7-1 victories against Charlie Lea and Steve Rogers, two of Montreal's finest, the Phillies extended their winning streak to seven and built their first-place margin to three games. That is the biggest lead for a National League East leader since the Expos were breezing by five in the pleasanter days of June.

The Expos, who entered the evening's action hopeful of sharing first place, dropped to third, four games behind the Phillies and one in back of Pittsburgh. Incredibly, they were dropping a doubleheader to Philadelphia for the second time in eight nights, the Phillies having leapfrogged the Expos into first with their sweep on Sept. 14.

"This was sweet," Owens said. "It's tough to do in the other guy's ballpark. I would have been certainly happy with a split. But the way we've been playing, the guys are confident. They feel they can beat anybody."

Except for having three runners picked off, the Phillies made few mistakes tonight. They got 28 hits in the two games and did not commit an error.

In the opener, Mike Schmidt's 38th homer broke a 1-1 tie in the third inning and the Phillies managed to stay in front the rest of the way, despite frequent counterattacks by the Expos. John Denny, although lifted after six innings and four runs, earned his 17th victory against six losses. Lea (15-10) was shelled for the second straight game after winning eight in a row.

Rookie Charlie Hudson, who allowed only one hit in his last start but was deprived of victory by two unearned runs, hurled a four-hitter in outduelling Rogers (17-11) in the second game. It was a 2-1 squeaker until the Phillies chased Rogers and most of the crowd with a four-run seventh.

There were a number of memorable moments in the opener, which required 3 hours 25 minutes.

Joe Lefebvre, the Phillies' right fielder who earlier threw out Andre Dawson trying to score from second on Al Oliver's single, hit a bases-loaded triple into the right field corner after Lea had intentionally walked Schmidt in the fourth. That made it 5-1, but the Expos battled back with three in the fifth.

Bob James and Len Matuszek were the protagonists in the seventh, when the Phillies boosted their advantage to 7-4. It was Matuszek who looked at three called strikes from James with the bases full a week ago, in the only one of five September meetings the Expos won from Philadelphia.

Tonight, with the bases loaded and two out, Matuszek lined a two-run single to right.

"I remembered," Matuszek said. "The last time I was caught with my bat on my shoulder and embarrassed. This time I went up there swinging."

Tim Raines' 10th homer trimmed the deficit to 7-5, but Ozzie Virgil's two-run homer off James in the eighth opened the gap once again for the Phillies. Then Chris Speier finalized the score with a two-run homer off Philadelphia left-hander Willie Hernandez.

"It was a barn burner," Owens said. "We had a lot of key hits and we still had to fight for it all the way."

In the second game, each team had one hit until the fifth, when the Phillies put together four singles for a 2-0 lead.

Montreal got one back in the sixth and had runners on first and third with one out. But Hudson retired both Terry Francona and Gary Carter on foul pops. For Carter, booed unmercifully most of the night, it was the fourth straight foul out in a zero-for-eight misfortune.

The Phillies sent 10 men to bat and broke it open in the seventh, creating a premature seventh-inning stretch for thousands of fans who left along with Rogers. Ivan DeJesus' single, Hudson's sacrifice, an intentional walk to Joe Morgan--who had five hits and is 13 for his last 18--and Matuszek's single produced the first score.

Then Schmidt's bat broke, the fat part sailing past Rogers' head while the ball hopped crazily over shortstop Doug Flynn's shoulder. Center fielder Dawson scooped up the ball in short center and threw it on the fly into the Phillies' dugout, allowing Matuszek to follow Morgan across the plate. After Lefebvre was purposely passed, Gary Matthews' single scored the fourth run.