The Atlantic Coast Conference athletic directors overruled, 5 nays to 3 yeas, yesterday their basketball coaches' weekend vote of 6-2 to adopt a 30-second shot clock.

Dean Smith, of all people, introduced the antistall measure on a one-year experimental basis and it seemed to be a case of when North Carolina's Mr. Coach proposes, the ACC disposes accordingly - until the A.D.s powwowed. They decided as N.C. State's Willis Casey, their outgoing chairman, put it, "We have a pretty good game now. "Why change it?"

The ACC wasn't saying how each school voted on the shoot-it-up or give-it-up proposition, and neither was Maryland (in the absence of the principals) saying whether its Carl James voted opposite form his coach.

In fact, said a Terrapin athletic department aide, "While the shot clock would be advantageous to the kind of teams Lefty Driesell has fielded, for all we know Lefty voted against it just because Dean Smith introduced it". . .

Sly Williams, Rhode Island's 6-7 All-East junior forward, and Cliff Robinson, USC's 6-10 All-West sophomore center, have renounced their remaining college hope eligibility and enrolled for the June 25 NBA draft. They join Magic Johnson and Garcia Hopkins to make a grand total of four available underclassmen.

So what luminary was left off the 1979 All-Star baseball ballots? Only Lou Brock-leading the NL in batting going into last night and still regularly adding to his 900-plus, all-time-most stolen bases. Blame it on the nominating committee of team executives, broadcasters and writers in his own town, St. Louis, who passed him up, even though this is his last hurrah.

The Redskin no-wobble nominee for the 1979 Byron R. White humanitarian award, the NFL Players Association's top honor; oft-honored Ken Houston. . .

The unemployed San Diego chicken, Ted Giannoulis, has gone to Seattle to talk turkey with the Mariners-about becoming an albatross?. . . And now it can be told: the 6-foot-8, shaggy-blue furry critter named Diplomaniac that cavorts as a mascot for the NASL team in RFK sometimes is Pat Sheehan, sometimes is Art Gallagher. They're Georgetown students, and the one tonight will have to work extra hard, since the Dips report the advertised fireworks by the great Zambelli has been postponed to the June 27 game with Edmonton, when school's out, no Bullets on TV.