Nothing frightens a plucky underdog team more than being brought face to face with its worst weaknesses under the eyes of the enemy.

The Baltimore Orioles need a deep draught of the waters of forgetfulness if they are to continue believing that they belong in the same high-rent district with the spoilsport Boston Red Sox after yesterday's 8-3 defeat.

The Birds flew into this cozy, inhospitable Fenway nest with 18 wins in 20 games. They have now had their tails salted twice - decisively. The hungry, healthy Red Sox seem intent on putting the American League East race to sleep, now.

Again today their muscle was apparent. Butch Hobson and Carlton Fisk homered, while that ancient sorcerer Luis Tiant, now 7-1, pitched a deceitful seven-hitter.

But Oriole sins were even more painfully on view. If starting pitching and short relief are the Baltimore strength, then defense, poor overall clutch hitting and long relief are the potential embarrassments.

"Like (former pitching coach, now Milwaukee manager) George Bamberger says, 'The Orioles have excellent defense . . . if you hit it to Mark Belanger,'" admitted Manger Earl Weaver before the game.

Yesterday even Belanger made an error, his first after 37 flawless games, throwing a ball into the Boston dugout on the fly. That was nothing compared to his teammates' blunders that undermined starter and loser Scott McGregor (8-5).

Fisk doubled on a high fly to right that the slow Ken Singleton simply did not have the speech to reach. Dwight Evans doubled (and eventually scored) on a high catchable fly to center that Larry Harlow misjudged backing off and letting the ball hit the base of the wall.

After McGregor was kayoed in the sixth, trailing only 3-2 with Sox at second and third and one out, he was sabotaged in absentia by reliever Joe Kerrigan and second baseman Billy Smith.

Kerrigan, a disaster in long relief all year (no wins, no saves, 5.60 ERA), walked the first two men he faced to force home a run. Then, on a potential inning-ending one-hopper behind second. Smith let Rick Burleson's grounder go off his glove for a two-run scratch hit and 6-2 Boston lead.

In the seventh the hijinks continued. Kerrigan walked the first two batters. One run scored when Belanger sired a double-play relay into Manager Don Zimmer's lap in the Boston dugout.

After a Kerrigan wild pitch, George Scott singled home Boston's last run. Just for garnish, Singleton lost another fly in the sun, played it into a single, then booted the ball for an error when he finally found it.

In a nice piece of reverse psychology. Weaver came off as totally unperturbed by it all. "This is a tough park to win in with pitching," he said. "And our outfielders were all breaking the wrong way for balls. That didn't help."

The Birds, now 8 1/2 games behind Boston, also chose the wrong times to hit their three home runs off Tiant. "So we're back to hitting solo homers," grumbled Weaver.

Rick Dempsey put the O's ahead, 1-0, with a third-inning liner to center that hit the horizontal yellow home run stripe on the wall that separates in-play from circle-the-bases.

Hobson answered with a blast over the screen in left, fair by a yard, in the bottom of the inning.

Eddie Murray opened the Oriole fourth with a monstrous 450-foot homer 20 rows up the right-field bleachers that would have made Ted Williams proud. Tiant, now trailing, 2-1, seemingly became unnerved and for the only time all day was on the ropes.

Singleton singled, Pat Kelly walked and Terry Crowley, singled, loading the bases with none out.

Tiant was one loud line drive from an early exit. But Doug DeCines (13 RBI in 183 at bats) bounced a 3-2 fast ball-down-the-pipe on the ground to third for a third-home-first double play.