The Washington Bullets yesterday placed guard Frank Johnson on the injured list and waived Guy Williams, Tom Sewell and Tony Costner, reducing their roster to the NBA's 12-player limit.

The Bullets will play their season opener in Atlanta Friday night.

Johnson, hampered by a broken bone in his left foot, is required to miss a minimum of five games, making him ineligible before Washington's Nov. 6 game against San Antonio.

"I think I'll be able to go by then," Johnson said following practice yesterday. "I could go now but it would be risky. The doctors feel it hasn't healed completely."

With Johnson out, the Bullets kept 6-foot-2 guard Perry Moss, who played in the Continental Basketball Association the past three seasons. He averaged 8.9 points in seven preseason games this year.

Guy Williams, a second-round draft choice in 1983, played in 21 games for Washington last season and averaged nearly three points per game. The forward had 34 points and 13 rebounds this preseason.

The Bullets traded a 1988 first-round draft choice for Sewell, a 6-foot-5 guard, after Philadelphia drafted him first in 1984, but he played only 87 minutes last season. He made 40 percent of his shots this preseason and averaged 5.7 points per game.

Costner, a 6-foot-10 center, opted to play in Italy last season after the Bullets selected him in the second round of the draft. He played 64 minutes in the preseason this year.

"We're a deeper team with (forward Dan) Roundfield, (rookie forward Kenny) Green and Manute (Bol, a rookie center)," said guard Gus Williams. "We have more team speed, and we're switching defenses better. We should have a better team this year, if we can avoid injuries."

Roundfield, whom the Bullets acquired from the Detroit Pistons in an offseason trade for center Rick Mahorn, is scheduled to have his injured left arm reexamined Thursday. Roundfield, who is on the 12-player roster, broke a bone in the arm during practice Oct. 4 and has not played since.