If any season tests the limits of mortal endurance, it's baseball's six months of systematic disappointment. For a contending team, the 162-game ordeal is a test of faith.

For the Baltimore Orioles, held to just a single by Rick Dempsey in a 6-0 loss to Toronto today in Memorial Stadium, these are the days when they're sorely tempted to become a team of doubters.

Rarely will a club go through a more emotionally draining experience than the Orioles did this weekend: in a 24-hour period they played three games that took them from elation to disgust. Just as they thought they'd finally begun to get their staggering season straightened out, the Birds suddenly find themselves stumbling again, two games under .500 (22-24) and painfully confused.

"We just can't seem to get over the hump," said Ken Singleton.

By the time the Orioles trudged off the field this afternoon to the grumpy boos of a crowd of 21,632, they had:

* Lost their first series here to Toronto in the Blue Jays' six years of existence. Heretofore, the Orioles had feasted upon the Jays with a 28-6 record in this park.

* Been beaten by rookie Jim Gott, who never before had won a big league game. Gott, a 22-year-old right-hander, allowed only Dempsey's clean line-drive single to left field in six innings before leaving with a stiff shoulder. His relief, Roy Lee Jackson, possessor of a 5-15 career record, faced nine Birds and retired them all without even a loud foul.

* Defaced a first-class pitching effort by Jim Palmer, who could have allowed only one run with better fielding behind him. A bases-loaded error by Lenn Sakata on what could have been an inning-ending double play grounder by Alfredo Griffin in the ninth opened the door for four gift runs for Toronto. Damaso Garcia followed with a two-run single and Garth Iorg got the final run with a ground out.

Palmer, who left quickly and without public comment, also was betrayed--as he has been so often in recent years--by his outfielders. Dan Ford produced a Toronto run by throwing to the wrong base in a two-run Blue Jay first inning and Al Bumbry played a catchable line drive into a ninth-inning double with some comic backpedaling footwork.

All this Oriole misfortune, however, probably should have been anticipated.

Occasionally, one game has such brutally depressing impact that it carries over and contaminates the next as well. That's what happened to the Orioles, whose spirits seemed thoroughly quashed by a morale-draining 11-10 defeat in the second game of a midnight-ending twi-nighter the evening before.

Throughout the clubhouse, both before and after this game, almost all conversation was about the previous night's second game. "If we'd won last night," said Manager Earl Weaver, growling, "this (defeat) wouldn't have meant a damn thing."

When, in Saturday's 11th hour, Benny Ayala pinch-hit a seventh-inning grand-slam homer to give the Birds a 10-9 lead, it was the electric shock that often arouses a team for a whole season.

"It seemed to send a jolt through everybody," said Mike Flanagan. "We were all really alive, maybe for the first time this season. In '79 and '80, we had games--one play, even one pitch--that seemed to turn us around. In '79, it was a sudden-death homer that Doug (DeCinces) hit. And, in '80, it was one pitch that Palmer threw to Reggie Jackson that got us out of an inning and won a game . . . Benny's homer had that same feeling. But . . . "

Instead, the Orioles' bullpen collapsed, again. Tippy Martinez walked the leadoff man in the eighth; he scored the tying run. Tim Stoddard then walked a man with none on and one out in the ninth; he scored the winning run.

"Those two walks are the kind of things that keep you from sleeping," said Weaver. "All year, our problems have, basically, come down to one department . . . we have not gotten the job done in short relief."

The Orioles' other worrisome area has been Weaver's tactics. Of the 11-10 loss, he said, "That was one of the greatest games I've ever managed, without a doubt. And that's what usually happens when I manage great. We lose . . . "

General Manager Hank Peters said: "Earl did some smart things Saturday night, but he also did a couple of things that maybe weren't so smart, like that intentional walk in the third inning (with the Orioles down by only one run), and taking out (reliever) Storm Davis after he'd pitched 4 1/3 shutout innings. The way our bullpen's been going, maybe you should stick with a hot arm when you find one."

For the teams that consider themselves contenders--like the currently struggling Orioles, Milwaukee Brewers and New York Yankees--the long season is a form of institutionalized water torture and collective team anguish. Day after day, 25 men are forced to face their recurrent inabilities, their misfortunes, their collective self-doubts. Each time, they're offered the psychic copout of caring less completely about the team's fate and, instead, merely punching the lucrative big league time clock and playing for their own statistics.

When Ayala's slam left Memorial Stadium, the Birds' resuscitation project was perfectly on schedule. They were on the verge of winning their 12th game in 16 against their current schedule of weak-sister opponents; they'd finally be back over .500 for the first time since opening day.

"We'd have been flyin'," said Singleton this evening. "Can't deny it."

Then, those blasted baseball realities that make a season so real, so hard, so compellingly revelatory of the characters on center stage, reasserted themselves. For the Orioles, like most of the teams in baseball in most seasons, the long laborious battle against self-doubt and dwindling faith continues.