BALTIMORE, OCT. 3 -- Not unexpectedly, the Orioles announced today that Manager Frank Robinson and his entire coaching staff would be back for 1991, the club's last season at Memorial Stadium.

"I'd like to be manager when the new stadium opens," Robinson said. "Like I said last year at this time, we've started something that would be tough to walk away from." . . .

Cal Ripken completed a remarkable defensive season, establishing major league fielding records for shortstops that should stand for years. Ripken made only three errors all season while handling 681 chances. That's a fielding percentage of .996, topping the mark of .992 set by Toronto's Tony Fernandez last season.

Fernandez made six errors in his record season. Over the last five years, major league shortstops playing regularly have averaged 18.1 errors a season. In his last 214 games, Ripken has made only four errors. He played in 1,446 of a possible 1,476 innings this season. He has played in 1,411 straight games. . . .

Two Orioles prospects who were given a long look in the closing weeks of the season have come up with injuries. Catcher Chris Hoiles has been told to rest his injured right shoulder for several weeks before beginning rehabilitation. He hurt himself making a throw to second Sept. 23.

Hoiles and the Orioles are puzzled as to why the shoulder went out, which for the time being puts a question mark next to his name. Switch-hitting first baseman David Segui strained his right knee bumping into a tarp in foul ground on Aug. 29. . . .

The Orioles finished with a home attendance of 2,415,189. Their best is 2,535,208 in 1989.