The Seattle SuperSonics pulled away from the travel-weary Washington Bullets late in the third quarter tonight and went on to a 105-87 victory before 15,542 at the Kingdome. The victory broke a four-game Seattle losing streak and improved their home record, the best in the NBA, to 21-4.

After the game was turned over to the reserves midway through the fourth quarter, the Sonics, playing their first game at home in 10 days, scored 14 straight points.

Gus Williams scored 18 of his game-high 26 points in the first period and the Sonics gave the Bullets only their third defeat in their last 10 road games and dropped them one game below .500 at 25-26.

The Bullets trailed by 12 points in the first half, but cut the lead to one point with 3:15 left in the third quarter. They then were outscored 8-2 to end the quarter and 8-0 at the start of the final period to fall behind, 84-69. They never got back in the game.

Greg Ballard led the Bullets with 17 points and Charles Davis, who played at guard for the first time this season, had 12. Jack Sikma scored 22 for the Sonics.

The Bullets will conclude this six-game, two-week road trip, their longest of the season, Saturday night in Oakland against Golden State.

Once again the team was without starting guard Kevin Grevey, who has injured ligaments and tendons in his right (nonshooting) hand and hasn't been able to play or practice since he incurred the injury in Dallas nine days ago.

Tonight's game was the SuperSonic debut of guard Phil Smith, acquired a week ago from San Diego for Armond Hill and a second-round draft choice. Smith hadn't been in uniform before tonight because his physical was delayed. He entered the game late in the first quarter.

The score changed 10 times in the first five minutes and neither side led by more than two points until the Sonics used an 18-4 run to take control at 32-20. Williams had 12 of those points, half of them on breakaway layups, and the Sonics ended the period with a 32-22 lead.

The Sonics don't run the usual three-on-two or two-on-one fast breaks. They like the one-on-zero type. Once the Bullet put up the ball, Williams would take off the other way. Whenever the Bullets missed and the Sonics got the rebound, they would pass the ball to a waiting Williams.

When that strategy didn't work, Williams was content just to stop and shoot from 18 feet.

When Williams sat down for a rest at the start of the second quarter, the Sonics stopped running and the Bullets made a charge. They cut the Seattle lead to 34-30 as Ballard, Rick Mahorn, Frank Johnson and Garry Witts scored, but Seattle settled down with a 10-2 run to get its lead back to 12 points. Fred Brown had four of the points.

The Bullets later got to within eight points in the half after a turnaround jumper by Mahorn, but Williams made one of two free throws for his 21st point of the half and Danny Vranes scored on a drive down the middle to give the Sonics a 55-44 halftime advantage.

Williams was the only player to score in double figures in the half.

The Bullets got a scare in the first quarter when Mahorn collided with Sikma, got kicked in the shin and went down in a heap, clutching his right leg. He had to be helped off the floor, but returned later in the half. Early this morning Mahorn had been told that his older brother was killed in an automobile accident Wednesday night.