As a writer who is completing a book on minor league baseball, I was most interested in The Post's Sept. 24 editorial "Baseball Near Washington," which concerned D.C. area minor league teams. Only recently, with the minors setting all-time attendance records, has it become clear that fans and non-fans alike have discovered baseball's previously best-kept secret -- games at which hot dogs cost $1 and the players, not yet isolated by fame, sign autographs by the dozen.

In the editorial, however, The Post stated that Class A is the "lowest rung of the minors." Contrary to conventional logic that "A" would naturally denote the beginning of any grouping, an even lower level exists. It is the traditional starting point for professional baseball careers, known as the rookie leagues.

The players at this classification are not only neophytes at baseball but at life as well, since many are 17- to 18-year-olds, away from home for the first time, living on $850 a month.

One rookie league, the Appalachian, sits at the confluence of Virginia, West Virginia, North Carolina and Tennessee. It boasts 10 teams, with several only a few hours from Washington near Roanoke in Southwest Virginia. The Baltimore Orioles have an affiliate in Bluefield, W.Va., although the team actually plays home games in nearby Bluefield, Va.

According to George Fanning, general manager of the Bluefield Orioles since 1954, more than 60 players have passed through Bluefield on their way to the majors. These players have included Cal Ripken Jr., Billy Ripken, Boog Powell, Eddie Murray, Don Baylor, Bobby Grich and Craig Worthington. It was in the rookie leagues that they received their first instruction in how professional baseball is played.

If the minors serve as baseball's school system, the rookie leagues are the first grade, where the lessons of the game are taught each year in places like Pulaski, Va.; Butte, Mont.; Johnson City, Tenn.; and Pocatello, Idaho.

So when the 1991 season rolls around, and you find yourself in some big league ballpark cheering on your favorites, take a moment to reflect on where it all began for those on the field.

BRUCE L. ADELSON Alexandria