Catcher Rick Dempsey blasted a three-run homer in the seventh inning today to cement Baltimore's 10-7 victory over the Toronto Blue Jays in a slugfest witnessed by a Halter Day crowd of 33, 572 at Memorial Stadium.

Dempsey fouled off two bunt attempts before his line drive hit the left-field foul pole, capping a four-run rally and giving the Birds a 9-5 lead.

The sweep of the four-game Blue Jay series sends the Birds on a 12-game road trip with a 5 1/2-game lead over Boston in the AL East.

The successful home stand, in which the Orioles won 10 to 12, pushed the team's mark to 22 victories in its last 25 games.

Nine extra-base hits, including home runs by Dempsey and Eddie Murray, provided most of the impetus today. Third baseman Doug DeCinces socked two doubles and drove in a run, and second baseman Rich Dauer knocked in two more. Center fielder Al Bumbry, who missed the last five games with a strained knee, and short-stop Kiko Garcia [a double and triple] each contributed three hits to the 14 Oriole safeties.

All of that offensive production was needed; Toronto, which had scored only one run in its previous three games, also had 14 hits. The Jays knocked out starter Jim Palmer after he yielded four runs -- two were unearned -- and eight hits in 4 1/3 innings.

Sammy Stewart pitched strongly until the ninth inning to get his fifth victory. Then Don Stanhouse entered to get the final two outs and his 10th save for abullpen that has only 14 this season.

"Jim came into the dugout after a couple innings and said, "I really don't have it today, give me a lot of runs,'" Dempsey said. "He didn't pop his fast ball real well. I've only seen that happen two or three times."

Perhaps the Orioles anticipated Palmer's plea. They registered three runs on RBI hits by Garcia, DeCinces and May in the first inning.

"Fourteen hits? It was about ti-i-i-i- me," crooned Oriole Manager Earl Weaver, who recently has seen more than his share of one and two-run Baltimore victories. "I'd ordered 15 hits, though."

Oriole owner Jerold Hoffberger, who almost weekly threatens to sell the club should it not draw 1.5 million home fans this season, was all smiles after assuring Weaver that Baltimore could hold on to its AL East lead. The Orioles are well ahead of that proposed attendance pace, having averaged 20,531 dates. That's an increase of 168,919 to the same point last season.

Can the Birds hold the first-place slot they have jealously guarded since May 18?

"Right now, I'm not making any predictions," Dempsey said. "Last season Boston blew a 14-game lead to New York, so anything can happen. But I think we have a stronger defensive team than the Red Sox had in '78. If we stay injury-free, we might do all right."

Dempsey's fourth homer of the season kept the Orioles moving. Twice, Toronto had rallied to tie, wiping out 4-0 and 5-4 deficits.

Designated hitter Roy Howell [three hits and four RBI] drove in two runs with a two-out single in the third. The unearned runs, snapping the Blue Jays 27-inning scoreless string against Oriole pitching, followed a booted ground ball by Dauer.

Toronto, loser of 12 straingth games to Baltimore, tied at 5-5 on Howell's run-scoring single in the fifth.

John Lowenstein and Lee May reached base on fielders' choices and Toronto reliever Jesse Jefferson contributed a throwing error to start the decisive seventh inning.

Lowenstein scored on Dauer's single, with May reaching third, and then Dempsey connected. CAPTION: Picture, Rick Dempsey