The Washington Bullets' slim chances of rallying from a 3-1 deficit in the NBA championship series probably hinge on how well they can defense Seattle SuperSonic center Jack Sikma in Game 5 Friday night at Capital Centre.

While teammates Gus Williams and Dennis Johnson are scoring almost at will in the back court, Sikma methodically has added enough points inside to give his team the decisive edge over the Bullets, who have yet to find a defensive technique to stop any of the Sonic marksmen.

Because it is difficult to double-team a guard, the Bullets cannot provide the help on Williams and Johnson that the Sonic have provided on Washington forwards Elvin Hayes and Bobby Dandridge.

But Washington can do a better job of trapping the steady Sikma, who has emerged as one of the NBA's better pressure players in his second proseason.

The Sonics have worked from the start of the series to isolate Sikma against Wes United and let their center either shoot over the Bullet pivotman or drive past him.

Despite intense defensive pressure from the sily Unseld, Sikma has improved his output every game and now is averaging 17 points and shooting 55 percent in the series while also pulling down 14 rebounds a game. In the last two contests, both Seattle wins, Sikma has scored 41 points, grabbed 34 rebounds and made 17 of 29 shots.

Almost every time the Sonics have needed an important basket, they have turned to sikma in the low post, relying on his unorthodox turnaround, step-back and release-behind-his-head jumper to produce needed points.

Ironically, the Bullets had thought the absence of Marvin Webster off last year's Seattle team would benefit them in the playoffs, especially after the Sonics lost center Tom LaGarde to injury during the regular season.

But Sikma, much more of an offensive threat than either Webster or LaGarde, has developed faster than even his own team officials had anticipated. He has become almost as assertive as Webster on defense (13 blocks in this series) and is much more dangerous on offense. And he is coping with Unseld's physical play much better than the more emotional Webster did last season.

The Bullets also have tried Hayes against the Sonic center and they have talked of using that matchup more often. But the coaching staff feels Unseld has done about as well as possible in trying to keep Sikma from scoring.

Sikma, a powerful 6-foot-11, 230-pound athlete known as "Banger" to his team-mates, is the main reason the Sonics are defying the accepted NBA axiom that championships aren't won by teams that get the majority of their points from the back court.

Without his reliable scoring, the Sonics would not have quite enough firepower in Williams and Johnson to subdue the Bullets.

But against his marksmanship, Washington constantly is guessing on defense. If Unseld or a Bullet forward switches off to help on Williams or Johnson, the Sonics are adept at dropping the ball off to Sikma instead of forcing shots. The result is a lot of high-percentage baskets by the Seattle center.

The rest of the Sonics are role players. Forward John Johnson leads the club in assists - he had 13 Tuesday - and is content to help set up the offense and let others socre. The other forward, Lonnie Shelton, and his replacement, Paul Silas, concentrate on defense and rebounding.

In contrast, Washington still is struggling to find its offensive continuity. Its two main scorers, Hayes and Dandridge, shot only 29 times Tuesday (scoring 34 points) while the Bulets worked diligently to help their guards shake off a shooting slump.

But the Washington back court still couldn't hit with accuracy. The guards made 19 of 54 shots, compared with 2, of 56 from Fred Brown, Williams and Dennis Johnson. And they were outscored 74-51, by the Sonic trio.

Hayes didn't play most of the fourth period when the Bullets were rallying from a seven-point deficit early in the quarter. Saddled with five fouls, he sat on the bench as Charles Johnson, with eight points, and Dandridge, with six, slowly rallied their team.

When Hayes did return, with 2:29 left in regulation, Seattle was up, 102-100. He picked up hsi sixth foul 116 seconds later after failing to add to his 18 points. He was a spectator when Unseld put in a rebound with 18 seconds left to send the game into overtime at 104 apiece.

Dandridge and Unseld also fouled out in overtime. The Sonics scored eight of the first 10 points in the extra period to grab a 112-106 lead and then held on as Washington again tried to pull even.

Williams and Dennis Johnson combined for those eight points, Johnson doing his scoring against the Bullets' smaller Charles Johnson, who missed two of three shots at the other end.

Baskets by Tom Henderson, Kevin Grevey and Phil Chenier, who was pressed into service after sitting out the first 52 minutes, surrounded two Sikma free throws and cut Seattle's margin to 114-112 with 30 seconds to go.

An air ball by Sikma gave Washington one last try with six seconds on the clock. Using a lineup of Chenier, Grevey, Dave Corzine, Greg Ballard and Charles Johnson, the Bullets tried to free Grevey for a shot. But he was triple teamed and his try was partially blocked by Dennis Johnson, who had five for the game.

"I probably should have put up a three point attempt (from 25 feet)," said Grevey. "I was open but then I dribbled into traffic. I was just hoping the shot would go in."

It didn't, and the 114-112 loss makes it necessary for Washington to win three straight games to pull out the series. No team has ever rallied from a 3-1 deficit in the championship round, although three teams, including the Bullets this season against San Antonio, have come back from 3-1 in earlier series.

The players talked bravely yesterday about making NBA history, especially the unflappable Hayes.

"I am positive we are going to come back," he said. "There is no question in my mind. We are the world champions. They are going to have to beat us; we aren't going to give this away.

"We are going to win Friday night and then come out here and win and force a seventh game.

"We had to win one of the three here (in Seattle) so it doesn't matter which one. It's hard to beat us three times on a courtt, we've proven that. I think what we did in this game shows we can beat them if we are allowed to play our game."

Grevey admitted it would "take a lot of luck and a lot of breaks, but it can be done. We just have to be reckless and go after it. We haven't got a thing to lose.

"I don't think there is anyone on this team who doesn't think we can do it. That's half the battle."

Yet Washington also realizes it gave Seattle an intense, relentless challenge Tuesday night, but still fell short. The Bullets never were in charge of that contest, which always seemed to swing on a Williams fast break or a Sikma jumper or a Dennis Johnson block. As long as Hayes and Dandridge aren't able to take charge, Washington's task remains difficult.

"It will be tough," said Dandridge. "Very tough."