The Seattle SuperSonics say they lost the National Basketball Association championship last year because they didn't have the strength inside to battle with the more physical Washington Bullets. They say that will not happen again.

So, with some clever manipulating and some ironic twists, Coach Lenny Wilkens has transformed his Sonics into perhaps the most physical team in the NBA. Yes, even more physical than the Bullets.

"I really like our team now," Wilkens said. "The experience factor has paid off and we have all of the physical strength we need."

The new-look Sonics finished the regular season with the second-best record in the league, after the Bullets, and until they ran into a bit of trouble in Phoenix the last two games, they looked like the class of the four teams remaining in the playoffs.

Their Western Conference final series with the Suns is tied at 2-2, but the Sonics say they are through fooling around and it will show in the fifth game of the series Friday at the Kingdome (WDVTM-TV-9, 11:30 p.m.).

"Maybe we took them too lightly after jumping away 2-0," Seattle forward John Johnson said. "We knew we didn't have to win down there, but we can't let them have a game here, either. Now we know we've got to win. It's a different story."

Wilkens is determined to get his team playing once again as he feels it should.

"Sometimes you turn the key just enough to get things going properly, then a guy takes a bad shot or makes a bad pass and you're right back where you started," Wilkens said. "We've got to cut that out."

To show he means business, Wilkens held a rare closed practice today. It lasted three hours.

The Sonics' game is not necessarily a pretty one, but it is effective.

Sometimes guards Dennis Johnson, Gus Williams and Fred Brown appear to just throw the ball up somewhere near the hoop, and if it doesn't go in, wait for one of their big rebounders, Paul Silas, Jack Sikma, Lonnie Shelton or Dennis Awtrey, to retrieve it for them.

"When you come down to pounding the boards in the . . . lane, I think we are as good as anybody in the league," said John Johnson, the Sonic's small forward. "We just pound, pound, pound. It's the makeup of our team. We're not a great shooting team, but we've got the people who do things necessary to win."

The Sonics have made four key personnel changes since last year, when they came within one game of winning the NBA championship.

Center Marvin Webster signed with the New York Knicks as a free agent, and the Sonics got a No. 1 draft choice, cash and Shelton, their power forward, as compensation.

The Sonics had three first-round draft choices in the upcoming draft, so they traded the worst of the three to the Boston Celtics for Awtrey, their backup center.

They acquired veteran guard Dick Snyder "as insurance" for two second-round draft choices.

They traded a No. 1 draft choice last season to Denver for Tom LaGarde, who was to replace Webster at center. After LaGarde injured his knee 23 games into the season, Sikma was moved to center and Shelton was made the starting big forward.

The Sonics no longer have a shot-blocking intimidator like Webster, but their rebounding is much better and they are physically intimidating.

"We used to be able to funnel the other team into the middle to Marvin," Wilkins said. "We don't have that luxury any more, so we have to funnel them to the side."

The Sonics have other luxuries, though, such as all that muscle inside.

Silas and Awtrey, backups to Shelton and Sikma, are not expected to score points. Their functions are to set picks, play defense, rebound, take up space in the lane and make their presence known by opponents.

Both are strong and intelligent and do their jobs as well as any backups in the league. The opposition usually pays a high price for any points it gets inside.

"Sometimes it just isn't worth the pain to go inside on them, so you get content in standing outside and shooting jumpers all day," said the Laker's Jamaal Wilkes, "and that's what they want you to do."

With LaGarde at center, Seattle won 17 of its first 23 games before he tore knee ligaments and was lost for the season.

Losing two starting centers - one as a free agent and his replacement to injury - would destroy some teams, but not the Sonics. Ironically, it may have made them better.

Wilkens had played the 6-11 Sikma at center and forward, so when LaGarde was injured. Wilkens moved Sikma to center permanently and made Shelton a starter.

"We felt comfortable moving Jack to center," Wilkens said. "He can rebound and shoot and he had experience at the position."

The Sonics are more versatile and physically stronger with Shelton at forward and Sikma at center.

"Everybody thought we wanted (Bob) McAdoo as compensation for Marvin," Wilkens said, "but I knew he (shelton) would fit in with our system. Shelton was the one I really wanted.

"I had seen him in college and I knew a lot about him.I just knew Lonnie would be a super forward. He was playing out of position at center with the Knicks and he was having some problem with it."

Most of the Seattle scoring still comes from the back court, where Williams averaged 19.2 points in the regular season, Dennis Johnson 15.6 and Brown 14.

Brown is recovering from a broken left hand and is averaging only 6.7 points a game in the playoffs. Williams is averaging a blistering 28.5 points, however, and Johnson 18.8.

The Sonics concede that Phoenix is playing well in this series, but like all good teams, they say their playing so badly in the primary reason the series is tied at 2.2."Right now we're thinking too much rather than just going out and playing basketball," Wilkens said. "We've become tentative and you don't win games that way. Our success comes when we make teams do what we want them to."

A Kingdome crowd of more than 30,000 is expected for Friday's game . . . The Suns said center Alvan Adams did not make the trip to Seattle because of his sprained ankle, but he is "hopeful" for the sixth game of the series in Phoenix Sunday . . . Phoenix has not won in Seattle since March 1977, having lost six in a row here . . . The Sonics have an 11-game home winning streak.