When the Orioles played their first game in Memorial Stadium in 1954, Dennis Martinez, Eddie Murray, Gary Roenicke and Sammy Stewart had not been born.

On Sunday, when the O's celebrate their Silver Anniversary, those four fledgling Birds, who are actually younger than their franchise, will be a primary reason why Baltimore has the best record (45-22) in baseball.

It is typical of the Orioles' recent progress, from gutty strugglers to strongmen, that they have produced waves of young, and unpublicized players, many of whom have done better in the majors than in the minors.

The four youngest Birds, all under 25, exemplify Baltimore's method of nurturing, improving and refining talent at the big league level - a sort of baseball finishing school.

This graduate school of hardball - the toughest kind of on-the-job training - has been a desperate force-feeding remedy for a team whose nest has been rifled by free agentry.

Baltimore, however, has proved uniquely ready to take young players under its wing - and win immediately.

It is no accident that Martinez, tied for the American League lead in wins (10-2), resembles Jim Palmer more in pitching strategy every year. The young Nicaraguan hangs on every word of Gentlemen Jim's. And there are plenty.

"Jim teaches me to be smart," says Martinez. "I asked him once, 'Hey, man, how do you make it look so easy? He told me, 'Listen and learn.'"

Also, it is no fluke that Murray, the team's most Valuable Player in 1978, can always be seen - in lobbies, on buses, in dugouts - talking to veteran Lee May.

Nor is it happenstance that Murray, exactly like May, is utterly phlegmatic - never complaining, playing hurt, performing best in the clutch because he is totally stoic.

"Their temperaments are almost identical," says a team coach, Jim Frey. "Eddie couldn't have a better example for the long, strong career he's going to have. Lee's the consummate professional."

If Roenicke looks a bit like a Frank Robinson clone - crowding the plate, hands held low and close, yanking homers down the line - it is no accident. Their lockers are side-by-side.

"Frank's all over him," said a grinning Manager Earl Weaver, looking at a statistics sheet that shows Roenicke is third in the league in slugging (.590) and second in on-base percentage (.446). "Robby and Frey have helped him get that Memorial Stadium stroke. And now Frank's got him, shall we say, 'anticipating' pitches."

What about Stewart, that jack-of-all trades who has made the O's pitching staff deep when it should have been weak with Palmer and Scott McGregor injured?

Ray Miller, the pitching coach, is a man that the 6-foot-3 Stewart shadows, asks constantly for advice and lays credit at the feet of. "Rabbit taught me the curve. I never had one until 31/2 years ago when he showed me," said Stewart, who had four more shutout innings of relief tonight. "Every mound I have ever been on in pro ball - from Bluefield to Puerto Rico to Yankee Stadium - Ray has been beside me"

The most dramatic, and vital, of the youth projects has been Martinez, who leads the league in innings pitched (125) and has a 19-6 record in his last 32 starts over two seasons.

"Dennis has gradually changed his thinking, a lot because of Palmer," says Dave (Boz) Skaggs, who has become Martinez' personal catcher throughout his current 10-game winning streak.

"He used to nibble too much, always go to a 3-2 count, even after he got ahead in the count," said Skaggs, whose calm disposition and humor are a better complement to Martinez' excitable temperament than the fiery Rick Dempsey.

"Now, Denny gets ahead of 'em and then goes after 'em, he never lets 'em back in the count . . . they never get even after he's got 'em 0-2. They stay defensive at the plate.

"Palmer has also taught him to keep the ball in the park, no matter what . . . gotta void those homers. Martinez now knows how to throw where their power isn't," Skaggs added.

"I'am going to pitching school," says the charming, always ebullient Martinez, who even seems coltish and jubilant on the mound. "I want to win easy games, like Palmer. Win when I pitch badly, not just when I pitch well.

"Last year, I had more strike'-emouts, but now I'm winning more. I've learned not to waste your best pitches for strikeouts when you don't need it . . . save the good pitches.

I thought that 'learning the hitters' meant learning to throw a perfect pitch in a perfect spot for a strikeout. Now I know that it means finding a pretty good pitch that gives you an easy fly ball or grounder."

"The only thing that can make Dennis even better," says Weaver, "is more knowledge. And he's getting it all the time."

Perhaps the most overlooked young star in baseball is Murray, 23, whose statistics show a May-like Xerox consistency - 27 homers in each of his first two years, 283 and .285 averages and 87 and 95 RBI.

"The similarity in his numbers is what shows you a real long career," says Weaver. "Look at all the great ones. Every season is a carbon copy of the others with small variations."

"It's hard to get up for 162 games," says Murray, who has missed one game in his first 389 Bird contests. "Heck, you can't even play 130 without being banged up most of the time. People don't know it, but hey man, there it is. They don't know how you gotta kick yourself in the behind to play."

Then Murray, who copies Mays lunchpail philosophy ("I just come to work every day"), finally breaks his sobersided expression. "I'd go crazy on the bench," says one of 12 children. "I just have to be out there."

Without doubt, the most dramatic Oriole reteaching process has been with Roenicke, another in a long line of Baltimore steals from Montreal that include Ken Singleton, Mike Torrez and Don Stanhouse. The Expos have a sign on their switchboard, Montreal officials joke, that says, "No calls accepted from Baltimore."

The O's checked with scouts who said Roenicke had great, but totally untapped power. "At line drives in the alleys," says Frey. "Nobody could get the big bull to pull."

But, this year, for the first time, Roenicke has lived up to his nickname - Rhino (rhymes with Roenicke).

"When I look at his stats, I try not to get too excited," says Weaver, looking at Roenicke's 13 homers and 35 walks in 165 at bats. "He's going to just the right people to learn. And he's doing just what Robby and Frey tell him."

"Doing just what Robby and Frey" say could be the motto of Baltimore's boisterous but fiercely analytical university of baseball: a team that is young, little-known, and, the standings say, the best in the major leagues. CAPTION: Picture, Doug DeCinces is congratulated by Billy Smith and John Lowenstein after game-winning, two-run homer in bottom of ninth. AP