Two of the knuckles on John Stefero's right hand are raw and ready to start bleeding again. The wounded areas are almost as big as dimes, as though he had been using a concrete wall for a speed bag.

The Baltimore Orioles' new third-string rookie catcher, just up from Rochester this month, has been getting a little too excited when he gets a chance to play.

It's not because he just helped the Orioles win two games. On Sunday Stefero hit a game-winning RBI single into right field to beat the Milwaukee Brewers in the ninth inning, and the next day he singled in the winning run in the 11th.

Stefero, 23, who was raised and lives in Baltimore, also played defense in the games; as he explains it, he's gotten so enthusiastic behind the plate, exhorting pitchers and pounding his fist in the catcher's mitt, that he's beaten his knuckles to a bloody pulp without knowing it.

Now that's a rookie.

Stefero is a perfect example of the infectious disease that has swept the Orioles in the past five weeks. After a certain point, events seem carried along by their own weight.

This evening in Tiger Stadium, during a rain delay, a dozen Orioles sat in their dugout and watched a scoreboard showing of "This Week in Baseball," relishing replays of recent victories in Yankee Stadium.

"Next week, it'll be Stumpy's turn," said a veteran, referring to Stefero's heroics as the rookie tried not to act embarrassed.

Stefero, who is 5 feet 8, 185 pounds, is a middle-echelon prospect in the Orioles' system. The team's catchers, Rick Dempsey and Joe Nolan, are 34 and 32. Stefero and Al Pardo, 21, are heirs to the job.

Stefero, originally a third baseman, has caught only since 1980 and is still developing as a receiver. He's shown at every level that he has some pop at bat. In '81 at Class A Hagerstown, Stefero had 25 homers and 82 RBI in just 338 at bats. In '82 at Charlotte in AA, he had 17 homers and 60 RBI in 357 at bats.

This season, Stefero improved again, returning to Charlotte and hitting .307 with 16 homers in 205 at bats--a true slugger's ratio. Used infrequently at Rochester, he hit .196 in 97 at bats. Such a hot or cold pattern is Stefero's modus operandi.

"I like his bat," said Joe Altobelli. "I like John 'cause he's that squatty-type catcher who can hit, like Yogi Berra." Naturally, the team has picked up on Altobelli's comparison and calls Stefero "Little Yogi" and "Young Yogi."

Because Stefero has been a bullpen catcher and midwinter backstop in the Memorial Stadium tunnel even when he wasn't on the big-league roster, he is especially well-known and well-liked for a rookie. Nonetheless, after his call-up Sept. 1, he didn't play for 18 days.

Now, as he pounds that glove and punches out game-winning hits, all that has changed.