The Washington Diplomats, seemingly an ill-fated team all season, received another blow yesterday when they learned that their leading scorer, Alan Green, has strained ligaments in his right knee and is unlikely to play in the opening-round playoff series against the Los Angeles Aztecs.

The Dips begin play in the NASL playoffs Wednesday at 8 p.m. at RFK Stadium against the Aztecs. The rematch is scheduled for Saturday in the Rose Bowl. Green will be on crutches through Wednesday and is unlikely to be ready by Saturday.

The 5-foot-7 English striker was bumped on the knee in Sunday's regular-season finale against the Minnesota Kicks but thought little of it initially.

Overnight, however, the knee swelled and Green was in considerable pain yesterday morning.He was examined by team doctor Carl Macartee, who diagnosed the injury as "a strained lateral colateral ligament."

Green was the fourth-leading scorer in the NASL during the regular season with a team record 25 goals and nine assists for 59 points, also a club record. He is the team's all-time leading scorer.

"The minute I saw him hobbling this morning I feared the worst," said Coach Gordon Bradley. "It's a terrible time for these things to happen but we can't afford to sit around and moan about it. We just have to pull up our socks and go out and play."

Bradley said he probably will start Mario Benito Luna, the young Argentine, in Green's place, opting for youthful enthusiasm over the experience of veteran Bobby Stokes.

"Mario's not proven yet he can score goals but he's shown the potential," Bradley said. "He's worked hard and hasn't complained about lack of playing time. We're taking a chance, but at this point we haven't much choice."

Luna has played in seven games since joining the team on loan in July, but has not started. He has not scored a goal in 165 minutes of playing time.

He is not nearly as quick as Green and has a tendency to carry the ball too much but Bradley said, "He's made progress in every practice. He's still only 21."

With Green out, Bradley said that Johan Cruyff, who finished the season with 10 goals and 20 assists, will have to think more offensively. But Bradley said he would not consider moving Cruyff up front because the midfield already is depleted by injuries.

Juan Jose Lozano probably is out for the season with a calf contusion; Sakib Viteskic pulled a leg muscle Sunday and is out; Thomas Rongen had a badly sprained ankle and is sidelined, and Carmine Marcantonio has a hamstring pull. The latter probably will play, but may not be able to last 90 minutes.

Bradley said he probably will move Gary Darrell from defense to midfield with Nick Mijatovic, who sat out Sunday with a back injury, returning to the back line to play with Wim Jansen, Bob Iarusci and Don Droege.

By contrast the Aztecs are completely healthy.

The Aztecs, second-place finishers in the National Conference Western Division, look to striker Luis Fernando for scoring.

Acquired last April from the first division club San Paolo in Brazil for a reported $300,000, Fernando has scored 28 goals in 28 games. Goalie Alfredo Ahnielo, acquired from Tampico in Mexico, has a 1.20 goals-against average.

On defense, Los Angeles' stalwart this season has been former Minnesota Kick Alan Merrick.

It is a strong club -- and, with a 20-12 final record, the best Aztec team ever.

"Losing Alan makes a tough job that much tougher," Bradley said. "He's been out best striker for two years.That's a lot to lose so suddenly."

The first day the Dips practiced in March they lost top defender Mike Dillon for the season. That set the pattern. It hasn't changed much.