The new-look Washington Bullets open their National Basketball Association season tonight at Capital Centre againist one of their most bitter rivals, the Philadelphia 76ers, and Coach Dick Motta is uneasy.

"I feel pretty good," Motta said. "But I'd feel better going into the season if we had Mitch (Kupchak). any conversation about our team and how well we'll do reverts to Mitch. We need him."

Kupchak, the Bullets' 6-foot-11 do everything sixth man, underwent back surgery in June and will not be able to play until some time next month.

"We aren't as solid a ball club right now as we were last year at this time because we don't have Mitch," said forward Elvin Hayes. "I think we'll have to make a lot of adjustments until he comes back and I think these first two games will really test us and tell us a lot."

The Bullets travel to Madison Square Garden Saturday to play the New York Knicks.

A crowd of 16,000 is expected for tonight's 8:05 game.

"No matter what happened in the first two games last year, we knew we would be okay because we were set at all positions and we had an edge because we knew what was going to eventually happen," Hayes said. "this year we don't know. There are still a lot of loose ends.

"We don't know yet how we'll make the adjustment to not having Mitch or how well we have adjusted to having Kevin Porter as our playmaker."

Porter's starting mate at guard is still uncertain. He will be either incumbent Kevin Grevey or second year man Roger Phegley.

Motta announced two days ago that Grevey had won the job, but Grevey's thigh was injured in practice Wednesday when he accidentally was kneed by Phegley.

The leg was stiff and sore yesterday and Grevey was listed as a questionable starter. If he cannot play, Phegley will start.

The front line, of Hayes, Bobby Dandridge and Wes Unseld, is the same as last season.

The Bullets got down to the 11 players NBA limit yesterday byby releasing rookie forward Garcia Hopkins from DuVal High School and Morgan State and putting rookie Steve Malovic and Kupchak on the injured list. Malovic has a sprained ankle.

A player on the injured list must sit out at least five games before he can be activated.

The only new Bullet now is 6-5 free agent guard Gus Bailey.

"I'd rather open the season against Philadelphia than anyone else," said Hayes, "because they are a free-wheeling type team. (Julius) Irving and (Doug) Collins do pretty much what they want and (Darryl) Dawkins is kind of that way, too. They have an offense that will really test us and I think we need a game like this to start off with.

"It'll really test our running game and with Kevin Porter being new, I think that's exactly what we need."

The 76ers are the Bullets' primary challengers for Atlantic Division supremacy and so this game will have a little more significance than most, even though it is only the first of 82 regular-season games.

When Collins was injured and out of the playoffs last season, Philadelphia Coach Billy Cunningham moved Erving to guard and started a front line of 6-11 Dawkins, 7-1 Caldwell Jones and 6-9 Bobby Jones.

Collins, one of the top shooting guards in the NBA, is healthy again, so Erving has moved back to forward. But Cunningham liked that big lineup so much he decided to sit Bobby Jones down and keep Dawkins and Caldwell Jones in the lineup together.

That is a strong rebounding team, but, surprisingly, the 76ers do not match up well with the Bullets, mainly because Erving must play Dandridge who gives him fits.

The other 76ers starter is superquick 6-1 guard Maurice Cheeks.

Hayes, who has been an all-star every one of his 11 years in the NBA, said he knows he will have to play more minutes and do more things until Kupchak returns.

But he also said he is prepared.

The Bullets were honored at the Touchdown Club yesterday and General Manager Bob Ferry was presented with a plaque naming him the NBA executive of the year.