NBA Commissioner Lawrence F. O'Brien said today that the winner of tonight's Bullet-Sonics game would play a best-of-nine series with the Portland Trail Blazers - as soon as Bill Walton's foot mends - to determine the "true" league champion.

"We have done an extensive survey." the commissioner said, "and discovered that 14 people in the country beyond the boundaries of the three cities involved still care about our playoffs.

"That looks like a grass-roots movement if I ever saw one."

Just a little tease for the crumpets, folks. Honestly, it's all over tonight, when either the Bullets or the Sonics emerge as champion of the NBA's annual test of fitness and greed.

The CBS ratings for the playoffs have been horrid, or about what one could expect from the longest-playing sports opera of them all. The NBA starts its season before the NFL is at midseason and now ends it after the major-league baseball season is one-third complete.

But two groups of Washingtonians, the state and the District, do not mind at all. They are poised for the sort of celebration that becomes even more special after so many seasons of frustrations.

The Bullets have been the most consistent playoff team in the NBA the last decade, always in but always out without a title. And Elvin Hayes was served a wire-service story, with his eggs and toast, yesterday morning that quoted his former coach, Alex Hannum, as saying:

"I hope Seattle wins the NBA championship. The Bullets have the individually superior players, but the Sonics have a group of guys who want to play. And Elvin Hayes is going to quit in the finals. Didn't he quit in the first game against Seattle? It was typical . . ."

Typically, this is a dreadful game to handicap, given the Bullets' history and the fact that the Sonics will not be remembered among the NBA's legendary teams. But the Sonics rely on outside shooting and they have not shot well from any distance the last 5 1/2 periods.

They do have one play that seems to produce a layup nearly every time they use it, however. Forward John Johnson flashes to the top of the free-throw circle, receives a pass and turns toward the basket.

By the time Johnson completes that turn, one of the guards, usually Dennis Johnson, has lost his defender on a pick near the right side of the free-throw line. So JJ throws a pass to DJ for an unguarded layup.

Still, anyone who has followed this series from the outset realizes that something unpredictable probably will take place. Neither team was supposed to make the finals in the first place and both have lost on their home court.

Playful witnesses have this fantasy: the game goes into so many overtimes that O'Brien calls for a soccer-like shootout to determine the winner. Everyone else has fouled out, so the shooters are Wes Unseld of the Bullets and Paul Silas of the Sonics.

Unseld and Silas are given 50 free shots each from the deep left baseline, with the man sinking the first basket winning the NBA title for his team. And the series still lasts until July 8.

In fact, those noted brick-throwers have been heroes. Unseld has kept a man six inches taller and much more mobile, Marvin Webster, relatively tame; Silas controls every important rebound - and often Hayes - in the final tense moments.

Both teams have regained fans that had drifted away, the Sonics after recovering so remarkably after a 5-17 start this season with several players who had little previous impact on the league.

The Bullets were certain they were among the very elite before the season, that the addition of Bob Dandridge was the final piece they needed for a complete team. Then Phil Chenier was injured. And Mitch Kupchak. And nearly everyone else at one time or another.

Healthy, they needed to at least make the Eastern Conference finals to woo back customers they had gradually lost since losing in the championship series three years ago to Golden State. They surprised everyone by winning the conference title over the media darlings, the 76ers.

The Bullets' owner, Abe Pollin, has spent as much time and money chasing a championship as anyone in sport. The Sonics' owner, Sam Schulman, is in the position of being one game from a title with relative rags after being so unsuccessful with rich acquisitions in the past.

"Whether we win Wednesday night or not," he said, "it's my personal feeling that the results have been incredible and we've won. To win it all would be superb, but win or lose we've made history and you won't find me that dejected."