After six months, countless practices and 81 regular season games, the Washington Bullets' playoff opponent will not be determined until their last game of the season today against the Philadelphia 76ers.

A victory at Capital Centre, combined with a New Jersey Nets loss in Boston to the Celtics, would give the Bullets and Nets 39-43 records, tying them for third place in the NBA's Atlantic Division. The Bullets would receive the higher sixth seed in the playoffs on the basis of their 4-2 season series edge over the Nets.

If that happens, Washington will face the 76ers in the best-of-five first-round series. If the Bullets lose or the Nets become the first team to defeat the Celtics at Boston Garden since Dec. 6, Washington would open the postseason against the Milwaukee Bucks.

"Now we just have to win. We can't worry about what other teams are doing," said Bullets Coach Kevin Loughery.

Although none of the Washington players openly will voice their preference, it's obvious they would rather face the 76ers than the Bucks. The most immediate reason is the injury to Philadelphia center Moses Malone, who broke his eye socket. The original diagnosis was that Malone would be able to play in the playoffs, but no doctor can predict how ready he would be.

Milwaukee Coach Don Nelson, a spectator at the Bullets' 105-103 loss Friday to the Chicago Bulls, said that he felt that Malone will play, "even if they have to put goggles on his face with little windshield wipers to keep the sweat out of his eyes."

Even with Malone's presence and no matter what the equipment, the Bullets believe that they stand a better chance against their divisional rivals. Today's game is the last of a season series that stands at 2-3 in favor of the 76ers. Washington has won both games at Capital Centre, by 21 and seven points. Even in the three losses at the Spectrum, Washington played Philadelphia tough, losing by five points in overtime, then 10 and seven points.

Washington was 2-4 against the Bucks this season. In their four victories over the Bullets, the Bucks won by an average of 17 points, including a 116-87 decision on March 18 that preceded the firing of Coach Gene Shue by a day.

The Bulls clinched a playoff spot with Friday's victory over Washington, although they will have the unenviable task of going against the Celtics in the opening round. In the remaining Eastern Conference series, Atlanta and Detroit, the second- and third-place finishers in the Central, will meet.

The situation in the Western Conference isn't nearly as muddled as that of the Eastern Conference. The top-seeded Los Angeles Lakers will begin defense of their 1984-85 NBA championship by facing the San Antonio Spurs. The second seed in the west, the Houston Rockets, will play the Sacramento Kings, one of the better teams in the league over the final month of the season.

The other two series are the Denver Nuggets against the Portland Trail Blazers and the Dallas Mavericks against the Utah Jazz.