Jeff Ruland, the Washington Bullets' all-star center and core of the team's offense, suffered a chip fracture of the right ankle against the Detroit Pistons Wednesday night and will miss the next six weeks of the National Basketball Association season.

Ruland, who is 6 feet 11 and weighs 275 pounds, also suffered a severe sprain of the ankle, according to Dr. Stephen Haas, a team physician. He put Ruland's foot in a cast yesterday and ordered him to stay at home and keep it elevated for the next few days. Ruland was injured in the final 34 seconds of the 108-100 victory over the Pistons.

"It's really frustrating, since we started to play well," Ruland said. "I just don't feel that great, but there's nothing I can do about it. I'm looking forward to getting the cast off. There will still be a lot of time left in the season to accomplish something."

Ruland said he was injured when Detroit rookie Joe Dumars drove the base line. Ruland went up in an attempt to block the shot and came down awkwardly on his right foot. "The next thing I knew, I was in a great deal of pain," he said.

As a result of Ruland's second serious injury in two seasons, Coach Gene Shue made two front-court changes in his starting lineup for last night's game against the Milwaukee Bucks. Manute Bol, the team's 7-foot-7 rookie center, made his first NBA start, and Dan Roundfield replaced Charles Jones.

Shue made the latter change "just to give us more offense in the lineup," he said. Bol, who already is a proficient shot blocker, is not an offensive threat, having scored only 30 points and taken 30 shots in 250 minutes before getting 18 points last night in the Bullets' 110-108 victory over Milwaukee.

Shue chose to start Bol over veteran reserve Tom McMillen, who started 20 straight games last season after Ruland suffered a shoulder injury that caused him to miss 43 of the Bullets' final 44 games.

"Manute has been doing a very good job for the team," Shue said. "He's better equipped to start."

Bol has gotten increased playing time recently and has 27 blocked shots in the Bullets' last three games. Ruland shared a ride from the airport with Bol yesterday and said he told the NBA's tallest player, "If you don't block 15 shots tonight, I'll be very disappointed." Bol blocked 12 shots last night.

Going into this season, it was said the Bullets had the best depth in the league other than the Boston Celtics and the Los Angeles Lakers. Now the Bullets, who were five games over .500 with Ruland last season and seven games under .500 without him, will find out how good that depth is.

"But you don't compensate for the lack of a Ruland," Shue said. "He was having an absolutely incredible season."

Ruland was named the NBA's player of the week Monday and twice in his past six games has produced double triples (at least 10 points, 10 rebounds and 10 assists in the same game).

For the season, Ruland is 17th in the NBA in scoring (21.2), third in rebounding (12.1), sixth in field-goal percentage (58.3) and the top center in assists (5.8).

"It's a tough blow at this time," Shue said of the injury.

"We started the season 2-7, and it was difficult to get things to work. We've really been playing terrific basketball; we've won eight of the last 11. Now, with Ruland getting injured, it's the most serious injury we could have because he's a player we use a lot in the offense."

Shue said the Bullets likely will sign a player to fill Ruland's roster spot. "We're still in the talking stages . . . who we might pick up and who might help us," Shue said.

"It's hard finding someone like that. We'll make that decision in the next few days. Most of the decent players are overseas. The players most recently cut are not good players."