The Capitals hired Jack Button yesterday and demonstrated anew they aren't fooling around about moving into hockey's power structure [spelled p-l-a-y-o-f-f-s].

Jack Button built NHL Central Scouting from the ground up the past four years; now leaves that office in Montreal to become the Caps' first director of player recuitment.

Button 39, was general manager of the Pittsburg Penguins from January 1974 to spring of '75, when he joined the league office. He supervised a 10-man staff whose reports, according to Washington General Manager Max Mcnab, "are a crucial factor in every club's evaluation of the junior crop."

With the Caps, Button's major responsibilities will be organization of the scouting system and assessment of junior prospects. On the latter, he ought to give the club a leg up come the Aug. 9 amateur draft, this year to include underage talent.

"The one thing you miss in the league office," said Button, "is the competitiveness, and I'm a competitive person." Capital . . .

Like the neighboring Yankees, soccer's Cosmos will find a way to make news. Giorgio Chinaglia and some teammates were practicising shots in Giants Stadium yesterday, hardly anybody around but some maintenance workers and security guards. One of the Cosmos missed a shot on goal. One of the stadium cleaners heckled. Chinaglia retorted, "You do your job, I'll do mine."

According to one guard, the janitor climaxed a shouting match with, "If you're so tough, come on up here," According to another Chinaglia began cursing and spit in the heckler's face. In any event, Chinaglia -- the NASL,S leading striker -- rushed into the stands only to be pushed over two rows of seats. Eyewitnesses said teamates David Brcic, Antonio Carbognami and Mark Liveric charged to Giorgio's assistance. Bric and Liveric jumped on the heckler; Carbognani allegedly went after another worker, who was swinging a shovel, and pushed him down a flight of steps. A third maintenance man got involved, and by the time order was restored, all three of the cleanup men had been injured badly enough to be taken to a hospital.

The soccer players all emerged unhurt. . .

James L. Denson, the D.C. Chamber of Commerce president who in his other hat as boxing promoter plugged hard to land the Coetzee-Tate heavyweight title bout evidently now committed to South Africa, now is after a welterweight championship bout. He is negotiating to match Jose [Pepino] Cuevas of Mexico, WBA titleholder, against Tommy Hearns, the undefeated Detroit youngster, in RFK Stadium in September. That's WBA, as opposed to WBC, in whicch sugar Ray Leonard-Wilfredo Benitez is the big item, Dec. 1. . .

Joe Gilliam, the ex-Steeler quarterback, has been sharpening up in Baltimore to beat the Colts in Pittsburg. Huh? It's Baltimore Eagles vs. Pittsburg Colts this very evening in a Mid-Atlantic Conference opener, with the semipro Eagles banking on Gilliam to bounce from down-and-out to the kind of QB they're missed since Maryland grad Al Neville hung 'em up after he led an unbeaten Eagle march to a Las Vegas bowl trip a couple years back.