Baltimore finished the first third of its season tonight with a dazzling 3-0, four-hit shutout by Dennis Martinez over powerful Kansas City that dramatized several of the first-place Birds' crucial improvements of 1979.

The O's, now 33-21, moved a game ahead of Boston as Martinez, who fanned nine and walked none, threw a sparkling 80 strikes in 118 pitches and intimadated a Royal lineup in which the first six batters all were hitting above .300.

"Dern," said Royal Manager Whitey Herzog with respectful brevity, "the kid kinda overmatched us, didn't he?"

Martinez's eighth straight win, all with lucky catcher Dave Skaggs behind the plate, was a crackling beauty in which he retired the first 10 men and had a two-hitter entering the ninth.

"I've never seen him with such control to go along with his raw staff," said Herzog. "He's definitely one of the best."

"He works the hitters like a young Jim Palmer," said Royal catcher Darrell Porter. "His stuff is a little different - a darting curve, not a big breaker, and a sinking fast ball, not a riser - but he has similiar ideas."

If Martinez, 8-2 with a 30.5 ERA in 104 innings, dominated this game from the first called strike to the final weak Porter dribbler back to the mound with men on the corners in the ninth, he got an assist from the Orioles' two biggest additions of the season - healthy Al Bumbry and Former Expo Gary Roenicke.

This pair has transformed the infamous Oriole outfield of '78 into a strength. When the O's traded Larry Harlow on Tuesday, it meant the final exodus of the spectral trio of Lopez, Harlow and Mora that haunts the memory of Baltimore fans.

After Lee May doubled home Rich Dauer, who had singled in the fourth, and Skaggs bloop-singled home Kiko Garcia, who had doubled in the fifth, Roenicke finished the Baltimore scoring with a solo homer in the sixth. Against Martinez, the 3-0 lead looked insurmountable.

"That Roenicke just added to the outstanding power that club already has," said Herzog. "Fans don't know how strong they are. They made our ballpark look small last week with the shots they hit. You make a mistake to Roenicke and it's gone."

Two nights ago, Roenicke, hitting .295 with 11 homers in only 132 atbats, poleaxed a homer that was only eight rows from the almost-unreachable top of the left-field bleachers. It climaxed a streak of seven straight Roennicke hits.

Tonight he crushed a Paul Splittorff changeup off the back wall behind the left-field bullpen fence. Few hitters can propoel a slop curve 400 feet. Roenicke started his home run trot one step from the plate, certain the ball was long gone.

If Roenicke's power, and his above-average defense, have turned left field, at least temporarily, from a wasteland to a garden, then Bumbry has redeemed center field with his .290 hitting, dozen steals and vastly more aggressive defense.

With one out in the ninth, Willie Wilson and George Brett, two red-hot hitters, each got his second single of the evening to put men on the corners.

Amos Otis, the Royal's top bat, scalded a liner to right center which a year ago, with the smooth but limited Harlow in center, would almost cerainly have been a triple - making the score 3-2 with a man on third with one out. Tension time.

Instead, Bumbry was off before the crack of the bat. "I got a rocking start, man," said the grinning Bee. "Nice jump."

With speed few center fielders can match, Bumbry simply outran the ball, as he has several in the last month, and snagged the ball on the dead run.

"Before this year, I probably wouldn't have gotten it," Bumbry admitted. "Frank Robinson (coach) has convinced me to play shallower, be more aggressive, take more chances. I'm playing offensive defense now, not worried defense. I'm concentrating on making good plays, not avoiding mistakes."

Ken Singleton made anothe fine catch in right tonight, another sign that the O's have finally decided to bear down on defense.

The fielding gem of the night, however, was a hidden jewel - Eddie Murray's scoop-and-flip to Martinez to nip Steve Braun on a leadoff drag bunt in the ninth.