This is the biggest night in the 11-year history of major professional sports here, but the upstart Seattle SuperSonics are playing it cool.

"We don't have anything to worry about," said guard Fred Brown. "Denver is the one that has to be worried. There's no reason for us to get all hyper. We have things just the way we want them."

This is the night Seattle can wrap up the Western Conference championship of the National Basketball Association with a victory over the Denver Nuggets. The Sonics would advance to the NBA final against the Eastern Conference-champion Washington Bullets. That seven-game series would begin in Seattle Sunday.

If Denver, which trails, 3-2, in this best-of-seven series should win tonight and force a seventh game it would be played Friday in Denver.

Most of the experts are saying, however, that even with David Thompson back in form, Denver doesn't stand much of a chance tonight.

The Sonics have won 19 in a row at the Seattle Center Coliseum, including seven straight playoff games before sellout crowds of 14.098.

The Sonics are in control of this series largely because of theie bench. With Paul Silas adding defense and rebounding up front and Brown providing a lift in the backcourt, Seattle is a very solid team. It hasn't always been that way this season.

Brown, a No. 1 draft pick from Iowa, has been with the Sonics for all of his seven pro seasons. No one else has been with the team for more than two years.

Brown began the season as a starter under Coach Bob Hopkins, but injured his knee and was not playing when Lennie Wilkens relieved Hopkins Nov. 30.

When Brown was ready to play, Wilkens sat down with him for a little talk. Wilkens wanted Brown to be his sixth man, to come off the bench and give the Sonics a spark. Not even Wilkens, however, envisioned the move working as effectively as it had.

The Sonics took off and Brown, always a feared shooter, because the highest-scoring nonstarter in the NBA this year with a 16.6 average.

He has averaged 17.2 points in 12 play off games so far.

"When I took over, the chemistry of our starting five just wasn't right," Wilkens said. "It wasn't a good blending of players and I wanted to change that immediately."

"Gus Williams had the speed and quickness to penetrate and get us running and Dennis Johnson was the big, strong quick defender we needed, and he played well without the ball. Johnson and Williams were a great combination right away and when Fred came back, I didn't want to change.

"I talked with Fred and felt he could help us best by coming off the bench," Wilkens added. "He agreed and said he just wanted to contribute."

Brown didn't look at it as a demotion. "I was just filing a role," he said. "The most important thing is winning and that was a way for us to do it better. That's the only way I could look at it."

Said Wilkens, "The objective of having Fred as a sixth man is to get us going, but you can do that in more ways thatn just scoring."

Brown is one of the game's great streak shooters, with his range seemingly unlimited - thus his nickname, "Downtown." Brown is never hesitant about putting the ball up, although his teammates don't consider him a gunner.

"He does other things beside shoot," Wilkens added. "In this series, he has come up with some big steals and assists. He was always capable of doing those things, but the other teams he played on didn't move well without the ball, so he had to do a lot by himself. Things are different now."

All of the hoopla about the scheduling of the finals, if the Sonics make them, hasn't gone to the players' heads. They know they still have to get by the Nuggets.

"We only talk about what's now," Wilkens said. "We'll be ready Wednesday night, no question."

"Begin ready" involves coming up with a way to control Thompson. The Denver guard exploded for 35 points in the Nuggets' victory Sunday to bring his team within one game of tying the series.

Thompson utilized screens from his teammates to elude Johnson and get off his jump shot.

Wilkens said his team wasn't mentally sharp Sunday and never helped Johnson when he got screened. "We weren't talking out there on the floor or anything," Wilkens said. "But we'll be sharp Wednesday night. I have no worry."