All are wanna-be's. One or two, if that, are will-be's. Sixty baseball players, in fine fettle and in their midsummer litheness, take a lap around the baseball field at St. Albans School. Their footfalls are light, as they should be. The earth these boys cover is the land of dreams, the dream of making it to the big leagues.

They have come, ages 16 through 22, at nine on a Sunday morning for a tryout with the Baltimore Orioles. In the next five hours, the athletes will showcase themselves like flower petals opening to July's sun. At midsummer, no spectacle in baseball offers the purity of a tryout. Innocence is here. Aspirations, not agents, are in control. Baseball, currently a game that needs to be kept playful, uses tryout camps as politics does the precinct ward. It's where the bosses spot the up-and-comings.

The Mayor Daley this morning is Jim Gilbert, the Orioles' scout who patrols the Mid-Atlantic states. This is his sixth tryout camp of the summer, with five towns to go. In an orange-and-white uniform with No. 68 on the back, Gilbert, 57, has a Yogi Berra friendliness and a Casey Stengel bent for baseball lore. A Baltimore policeman for 25 years before trading uniforms, the scout recalls that his father was born the same year and in the same neighborhood as Babe Ruth. Everyone around on Mulberry Street in Baltimore could see that the young urchin, George Herman Ruth, had a baseball future: ''My father said that when the Babe was a kid and you played in front of a bar with swinging doors he would throw a beer bottle at you.'' Babe, lorists will tell you, was a pitcher before becoming a slugger.

Between tales, Gilbert occasionally calls across the St. Albans field to someone named ''Stretch.'' At 6-feet-8, wearing an Oriole uniform with Williams on the back, this is the assistant scout. He would be a natural for the role of a barking drill sergeant, with these 60 shavetails around him. It's the opposite. He is brotherly with them. A joke is shared with one, encouragement with another. If these were George Bretts or Dave Winfields, respect wouldn't differ.

Stretch Williams, 29, carrying a clipboard and balancing a pencil between his cap and ear, covers ground like a shortstop. He goes from the outfield timing running drills, to the infield looking for the good glove, then to the bullpen calling up pitchers to take their turns. Like Gilbert, Stretch's father has a baseball connection. He's the Orioles' owner, Edward Bennett Williams, and likely at this moment on his knees at Sunday Mass praying for a miracle that his team will finish higher than last place.

God's work at the St. Albans field is about the talent He dispensed and where it may lead. From the 29 outfielders, 14 pitchers, 12 infielders and five catchers, Gilbert's eye is on ''follows.'' These are the lads who will throw, hit or catch a ball today with a skill that looks as if the ball will be thrown, hit or caught much, much better tomorrow. They rate a follow-up. They'll be tracked like banded whales through the seas of college or summer league ball.

Gilbert, in a craft known as ''ivory hunting,'' has every player today fill out a ''Baltimore Orioles Registration Card.'' He and the team's 13 other scouts, as well as the scouts for the other 25 teams who also use the 30-member major league scouting bureau, collect thousands of cards every year. Gilbert also keeps mental cards. He has a follow in ''East Carolina, a burly guy who looked like he'd been carrying around telephone poles half his life.'' Another is a pitcher ''I saw yesterday throwing 85 up in Frederick. He looks pretty good for next year.''

The bright news about tryout camps is that 80 percent of the 624 players currently in the big leagues came through them. The dark side, said Gilbert as he stood behind second base watching the shortstops turn double plays, is that only a few players are signed and only 5 percent of that small number get out of the minors to the majors. Gilbert, whose bushy eyebrows are as orange as his Orioles jersey, says that it takes a stupendous blast to the outfield or a curve ball that breaks a yard to impress him: ''Some guy can show you good tools here and gets in a ball game and can't play at all.''

Despite the gummy heat, Gilbert stays coolly alert. Divinations are jotted. Stretch Williams, tending the family store, thanks players individually for coming. The lads, their mitts and dreams both oiled, go home. Half a century from now, they'll be telling their grandchildren about the day long ago when they had a tryout with a big league team. The tale will be true. Scout's honor.