n an effort befitting their proud tradition, the Boston Celtics refused to give up their championship tonight, bouncing back once more to force a sixth game in the NBA Eastern Conference final by routing Philadelphia, 114-85.

Taking a big lead in the second quarter with a stretch of intense defense worthy of being shown in the Hall of Fame, the Celtics came close to duplicating their 40-point margin of victory in Game 1 here 10 days ago.

Robert Parish, the scoring leader of the semifinal series against Washington, came back from two subpar performance to pace the Celtics with 26 points, 10 rebounds and three blocked shots. Larry Bird, struggling with his outside shooting lately, scored 20 as Boston's offense regained its familiar regular-season style and effectiveness.

Coach Billy Cunningham, still troubled by the 76ers' performance last year, when they lost the last three games after being up in the series, 3-1, now must regroup his players for Game 6 Friday night in Philadelphia.

"Boston came out physical tonight and we'll come back the same way Friday," Cunningham said. "The key was their defense. They double-teamed Andrew (Toney) and we didn't move the ball very well to get the open shot."

Toney, who scored 30 points in one Philadelphia victory and 39 in another, was held to three field goals in the first half by tenacious double-teaming and never got into his game. He still finished as the 76ers' top scorer with 18 points, but made only six of 20 shots.

The Celtics were able to dominate this game from beginning to end because they again used their size and strength to advantage around the basket. They outrebounded the losers, 15-6, in the first quarter, setting the tone for the evening. They finished with a 64-49 advantage.

The game was won in the second quarter when they Celtics' pressing defense harassed the 76ers into poor shots and turnovers. Boston made only eight of 20 shots, yet outscored the visitors, 24-15, as Philadelphia sank a mere four of 26.

"Our defense in the second quarter was as good as we've played in the playoffs," Coach Bill Fitch said. "We were more aggressive and we recognized the double-team situations when they were available. We worked harder against Toney."

In addition to defense and rebounding, Fitch and several of the Celtics credited two days of practice since Sunday's 119-94 loss in Philadelphia as a major factor in the Celtics' reversal.

"We needed those days of practice to adjust being without Tiny (Archibald)," Fitch said. "He's a unique type of player and it takes time to adjust our timing without him."

With Archibald out because of a dislocated shoulder, Gerald Henderson is in charge of the Celtics' running game. In 38 minutes tonight, he had 15 points, six assists and committed just one turnover.

"I felt a lot more comfortable out there tonight," Henderson said. "We had a game plan that was based on me running the team and I think that helped all of us.

"Defensively, we applied a little better pressure, we picked them up earlier and forced them out of what they wanted to do."

If the Celtics play Friday in Philadelphia as they did tonight, they will answer the pleas of the sellout crowd which chanted "See ya Sunday" at the 76ers throughout the closing minutes of the rout. If a seventh game is necessary, it will be played here Sunday afternoon.

It didn't take long for Boston to establish dominance in this one. After three early ties, the Celtics scored 10 straight points as the 76ers went almost four minutes without a point.

One of the pregame plans was to get Parish involved early, and he responded by making his first six shots. He had six of the Celtics' first 16 points on three high-arching jumpers and a jam. He had 10 points in the first seven minutes as Boston took a 24-14 lead.

Darryl Dawkins replaced Bobby Jones at that point as Philadelphia tried to match the Celtics' aggressive rebounding. He scored four quick points and Julius Erving (12 points) added six, but the rest of the 76ers went scoreless in the final five minutes of the quarter.

With Parish scoring five more points, giving him 15 for the quarter, Boston widened its advantage to 33-22 heading into what the decisive second period.

Playing with the intensity usually reserved for the final minutes, the Celtics were picking up the Philadelphia guards near midcourt, double-teaming whomever had the ball, hand-waving, bumping and fighting through picks in a manner that frustrated the 76ers.

"They forced us farther out, double-teamed, then covered the open man," Bobby Jones said. "We just couldn't get into our offense."

Toney, the key to the 76ers' offense, was held without a field goal in the quarter and there was nobody to fill the void. The Celtics were in command, 55-37, at intermission.

From then on, Boston could afford to simply trade baskets and coast to its first victory after three successive defeats. The Celtics have not lost four in a row since Fitch became coach three years ago.

Of the Celtics' victory, Erving said: "All it means is that they have to win two games instead of three."