The Seattle SuperSonics are in position to win the West today in their National Basketball Association playoff series with the Denver Nuggets.

Seattle leads the series, 3-1, and a victory would move the sonics into the championship series against the Washington Bullets, the Eastern Conference champions.

There is one observer who believes Seattle will be hard-pressed to clinch the series in Denver.

He is Larry Brown, the Denver coach, who says, "That game Sunday is in the bag. You can court on it. There is no way Seattle will beat us in our place."

The Sonics are confident, Coach Lenny Wilkens says, but not complacent.

"We don't have overconfidence. I'm getting tired of that suggestion. Our guys go out and play hard, they know they're playing a good team. This is a very good ball club and we know we've got to be at the top of our game to beat them."

If Seattle is to win, it must continue to play the excellent defense it displayed the last three games, especially Friday's. In the second half of game four, the Sonics yielded just 36 points, 18 in each quarter.

And the Sonics must continue to contain Nugget star David Thompson, who has been held in check by Dennis Johnson.

Johnson harassed Thompson into a 10-for-27 shooting night Friday.

Johnson's defense prompted Sonic forward Paul Silas, a veteran of 12 playoff years, to comment, "I played with Denver a whole year (last season) and I've never seen anybody play David like he did."

It was the game of Johnson's life: a career-high 31 points, six rebounds, three assists - and defense against Thompson, who in the final game of the regular season poured in 73-points in Detroit.

Eighteen of Johnson's points came in the second half, when Seattle rallied from a 58-50 deficit and won its 19th straight game at home.

If Denver is to win, it must solve Seattle's defense - second best in the league during the regular season - and restrain its guards.

Denver must find a way to maneuver past Seattle center Marvin Webster, who rejected five shots Friday and has 19 blocks in the four games.

Seattle's guards, Johnson, Gus Williams and Fred Brown, have shredded the Nuggets for 215 points and taken control in the fourth quarter in the last three games.

Johnson has scored 79 of these points, Williams 69 and Brown 67 as a reserve.