The National Basketball Association playoffs begin tonight, starting a two-month ordeal to determine the league's champion. Staff writer Paul Attner examines the matchups in both the Eastern and Western conferences and predicts the probable winners.

Paul Silas may be old, slow and a horrible leaper but he remains the best reason why the Seattle SuperSonics should get another shot at the league title.

Silas, much like his team, is unspectacular but solid. He also is a winner who makes a habit of playing on clubs that reach the elusive title round.

In an otherwise unpredictable, wonderfully competitive Western Conference playoff picture, he emerges as the one major difference between the Sonics and the competition.

"You just don't bet against a Paul Silas team," said Seattle Coach Lenny Wilkens. "He has a way of playing on winners."

The Sonics were surprised last season to be in the finals against Washington. This year they expect to advance that far, although they might have made a horrible mistake.

They failed to reserve enough playoff dates in the Kingdome or last season's home court, the Seattle Coliseum. Now they may have to play two semifinal-round games in the University of Washington's Edmundson Pavilion.

Last year, they could have lost the title to Washington when they were forced to move one game to the Kingdome. The Bullets won that game, the pivotal contest of the series.

Seattle depends heavily on guards for the bulk of its offense, a dangerous situation in the playoffs. But center Jack Sikma has come on so strongly this year that he and strongman-forward Leonnie Shelton make the Sonics more formidable inside than they were last season.

Dennis Johnson, who is playing out his contract, is the best defensive guard in the league and a dangerous scorer in the clutch. Gus Williams has averaged 25 points the last quarter of the season at the other guard and Fred Brown is, well, Fred Brown-one of the NBA's best pure shooters. But Brown's ring finger on his left hand is broken and he will miss several early-round games.

Yet the Sonics are not that much stronger than Phoenix. and Los Angeles always is a threat as long as there is any chance Kareem Abdul-Jabbar will motivate himself for the playoffs.

No one is sure what Midwest Conference winner Kansas City will do in the playoffs. The Kings rode on Phil Ford's shoulders most of the schedule before a late-season injury to Scott Wedman almost cost them the divisional crown.

Ford has never been through the emotional rigors of the NBA's second season, which should neutralized some of his talent. Yet this exceptional palyer keeps surprising everyone with his poise and his uncanny ability to set up teammates, especially fellow guard Otis Birdsong, for open shots.

If Phoenix gets by Portland, the Suns would have the home-court advantage over Kanasa City in the semifinal round, which should be enough edge to get them into the conference finals.

In the other semifinal, the Sonics have too much talent for injury-slowed Denver. Los Angeles is another question, although the Laker guards should not be good enough to handle the likes of Williams, Johnson and Brown.

A Phoenix-Seattle matchup in the conference finals would be a dandy, but the Sonics have been too physical for the Suns to handle this season. To win, Phoenix would need a quick comeback from Truck Robinson, who still hasn't recovered from a late-season illness.

Portland (45-37) Versus Phoenix (50-32)

Any team starting a 6-foot-10 player at small forward shouldn't be good enough to make the playoffs. At least that is the conventional thinking around the NBA, where this kind of wild experimenting is considered a sign of weakness.

Yet Portland is int he playoffs only because Jack Ramsay took a chance and benched Bobby Gross, a starting small forward on his title team two years ago. Taking Gross' place was rookie Mychal Thompson, who Ramsay says is one of the best defensive players-at any position-in the league.

With Thompson in the lineup, the Trail Blazers stormed through the last part of the schedule, getting most of its scoring and rebounding from a front line of Maurice Lucas, Tom Owens and Thompson.

This trio, led by the dangerous Lucas, will attack the Suns' most obvious weakness, lack of inside strength.

Ironically, Phoenix played better the last two weeks with Gar Heard at big forward instead of Robinson. The Suns are a finesse team that relies on quick movement, the scoring of Walter Davis and Paul Westphal and the steady play of center Alvan Adams, who is coming off his best season. Robinson interrupts their offensive flow and especially hinders Westphal, whose scoring average dropped after the trade.

This series seems certain to go three games, since Portland rarely loses at home. That means the Trail Blazers, so finely tuned by Ramsay, have two shots to knock off the Suns at Phoenix, where the home club is not that formidable.

Los Angeles (47-35) Versus Denver (47-35)

The Nuggets activated George McGinnis, who is out with a bad ankle, for the playoffs but he won't be ready for at least another two weeks, probably longer. So Denver must try to beat the Lakers with six players and a home-court advantage, which still may not be enough.

Denver performed more consistently after McGinnis was hurt, making a marvelous run at Kansas City for the Midwest crown before losing on the final day of the season. But the Nuggets need his talent to be competitive for any length of time in the playoffs, since his absence all but destroys an already questionable bench.

David Hompson, again the focus of Denver's offense, must have an outstanding series if the Nuggest are to beat Los Angeles.

Los Angeles has embarrassed by Seattle on national televisioon Friday night, then beat both Portland and Phoenix the next two games to revive Coach Jerry West's hopes.

West has benched Adrian Dantley, slowed by a sore ankle, and will start Don Ford, a better defensive player, against Denver. But he still can't solve the Lakers' shooting guard problems (Lou Hudson, Ron Boone and Jim Price all are in slumps); nor does he know how Abdul-Jabbar will react to these playoff games.

If Abdul-Jabbar feels like playing, he can compensate for a team full of headaches. If he doesn't, Denver will win the series. CAPTION: Picture 1 through 4, Playoff luminaries: Kareem Abdul-Jabbar, left: John Drew, top: Julius Erving, bottom: Maurice Lucas, right. Photos by Richard Darcy-The Washington Post and AP; Picture 5, Dick Motta