The Washington Bullets will learn a lot about themselves in the next 48 hours when they twice challenge the Philadelphia 76ers.

The first game is at 8:05 tonight at Capital Centre, with the return match in Philadelphia Sunday night.

The 76ers (51-9) have the best record in the National Basketball Association, but the Bullets gave them one of those losses, 100-97, at Capital Centre Dec. 18. The 76ers are the only team with a playoff spot already assured and are now merely chasing immortality. They have a shot at the NBA record of 69 victories in a season.

The Bullets, meanwhile, have more pedestrian goals, such as getting into the playoffs.

The Bullets (27-32) are tied with Detroit (29-33) for the seventh-best record in the Eastern Conference. Atlanta (32-31) and New York (31-30) are tied for fifth. The top six finishers qualify for the playoffs.

The Knicks host Portland tonight and the Hawks play the Pistons at the Silverdome.

The Bullets have won three in a row, but may play tonight without two starters, forward Greg Ballard and guard Frank Johnson. Ballard has a chronic back problem and scored only six points in the last two games. He hasn't practiced for two days and his playing status won't be known until just before game time.

Johnson has been hobbling for three weeks on a jammed big toe. He didn't play in the last game and also is questionable for tonight's game.

If they can't play, Charles Davis, coming off a career-high 21 points against Chicago Wednesday, will start for Ballard. Don Collins will start at shooting guard, with Ricky Sobers taking over Johnson's point guard position.

The Beef Brothers, Jeff Ruland and Rick Mahorn, are healthy, though, and how well the Bullets do this weekend will depend a great deal on them. They have been the mainstays in the three-game winning streak, combining for 148 points and 72 rebounds while shooting 69 percent.

Mahorn, who was in a slump before the winning streak, has averaged 21.3 points and 13.3 rebounds. Since Ruland was made a starter nine games ago, he has averaged 27.9 points and 12.1 rebounds and has shot 63 percent.

It likely will take both of them to slow Moses Malone. He had 34 points and 23 rebounds in 37 minutes in a 123-114 Philadelphia victory over Detroit in his last game.

Before that game, the 76ers had lost two in a row for the first time this season. Malone is their leading scorer at 24.5 points and is the league's top rebounder at 15.7. Julius Erving is averaging 22.2 points and Andrew Toney 19.2.

The other Philadelphia starters are Marc Iavaroni and Maurice Cheeks.

Forward Bobby Jones has missed the last four games with a fractured toe, but may play tonight. In his absence, 6-foot-10 Clemon Johnson, who came to the 76ers from the Indiana Pacers 10 games ago, has picked up the slack. The backup at center and power forward, Johnson has averaged 8.6 points and 5.6 rebounds.