PAI day is here - a material step toward One Big Union of athletes.

Sports unions in six leagues, meeting here have formed an umbrella organization named Profesional Athletes International, with prime mover Ed Garvey, the NFL Players Association executive, as staff director. Some 2,700 members are initially involved (or will be when their $10 initiation fees are paid): 1370 NFL players, 500 North American Soccer Leaguers, 315 Canadian Football League players, 250 from the Association of Tennis Professionals, 175 World Hockey Association players and 100 Professional Riders (of motorcycles).

The NHL and NBA players unions said thanks but no, Garvey reports, but the Ladies PGA and Women's Tennis Association are interested - and the major league baseball players reps may consider membership when they meet July 11 during the All-Star break.

As is, Garvey figures two-thirds of North America's pro athletes are in the PAI, whose first project will be an information exchange newsletter. Possibilities for cooperation are endless, Garvey ventured, such as joint insurance programs, better preparation for collective bargaining - "Several of the sports leagues [on the ownership side] have the same lawyers, so there's no reason we shouldn't, too.They know exactly what's been going on in every sport, whereas we've developed separately" . . .

Perhaps a persuasive nudge toward baseball's union grabbing for more clout is the way National League's clubs are making good as Opening Day nears on their "individual" decisions to cut down to 24-man rosters against an authorized 25. That's a dozen major leaguers becoming minor leaguers (although management will tell you it's better they're playing every day than warming benches) . . .

NASL tallied 205,557 soccer customers at the weekend season openers, a record average of 20,556 compared to 10,750 a year ago. The Dips' home bow, coming up Sunday against the Chicago Sting, could mark the virtual unveiling of goalie Bill Irwin; so dominant was Washington in the 3-0 win at Philadelphia, he was called upon for only four, nonscary saves. But a shutout's a shutout . . .

Tom Apke, after pulling out of the running for the U. of Cincinnati post in his hometown, has told Purdue to forget him as a candidate for basketball coach, he will renew his contract at Creighton - "I cannot leave those kids. I just cannot leave the Creighton family" . . . The Providence-area media who gathered Friday to meet Brown's new basketball coach, only to learn that Indiana assistant Bob Donewald had backed out at the last minute, assembled at Marvel Gym again yesterday - this time to meet the new Bruin coach, Joe Mullaney, by telephone. The old Pro (six teams) and Providence College (271 wins) coach tried to keep it short, at $18 a minute from Italy, where he currently is coaching a pro squad . . .