The Los Angeles Lakers had their fast break working tonight and used it an balanced scoring to offset a 39-point performance by San Antonio's George Gervin and defeat the Spurs, 118-108, for commanding 3-0 lead in their National Basketball Association Western Conference championship series.

The Lakers, who are 7-0 in playoff games this year, can clinch the series here, at HemisFair Arena, Saturday night.

Karem Abdul-Jabbar had 26 points and Norm Nixon 22 for the Lakers.

San Antonio Coach Stan Albeck said before tonight's game that his team would go to Gervin early and often, and that's what the Spurs did. Gervin, the NBA's regular-season scoring champion with a 32.3 average, had only 18 points in the last game, but got 10 in the first eight minutes tonight and the Spurs were ahead by two, 18-16.

But Nixon took over, though, and showed why many feel he is the best point guard in the league. He led the Lakers on a 13-4 spurt that put them on top, 31-24, a minute into the second quarter. Nixon had five points and three assists in that spurt as the Lakers were off and running at every opportunity.

Gervin also had six rebounds the first period, but he wasn't much of a factor the rest of the half. He was called for his third foul three minutes into the second quarter.

The Lakers' fast break was so devastating that 16 of their first 23 points in the second quarter came from fast-break baskets. They seemed to continually have three-on-two, two-on-one and three-on-one opportunities, and they took advantage of every one.

Seven straight points, all off the fast break, hiked the Lakers' lead to 12 points, 49-37, with 4:20 left in the half. Abdul-Jabbar started the spurt with a three-point play as he was fouled by Mike Bratz. Magic Johnson then stole the ball from Gervin and started a fast break that ended in Jamaal Wilkes' basket.

Wilkes made another shot after Mike Mitchell missed a jumper for the Spurs and the Lakers' lead grew to 61-46 on Bob McAdoo's free throw with 46 seconds left in the half. Gene Banks scored on a fast-break dunk at the buzzer to reduce the Lakers' advantage to 61-48 at halftime.

Because they were getting so many fast breaks, the Lakers made 50 percent of their shots that half while the Spurs shot 36 percent, having made only 10 of 30 shots the second quarter.

Gervin had 16 points that half, to lead all scorers, but he made only five of 13 shots. Abdul-Jabbar had 15 points and Nixon 14 for the Lakers, and they made 10 of 14 shots.

Gervin came out firing after intermission, scoring first on a left-handed driving hook, then on a similar shot to his right. He capped his three-minute flurry with an 18-foot jumper.

Nixon stayed with Gervin basket for basket, though, hitting three straight 18-foot jumpers, and they kept the Lakers ahead by 12, 69-57, with nine minutes left in the quarter.

Two minutes later, after a series of missed shots and turnovers by both teams, Mitchell scored with a rebound, then George Johnson stole Magic Johnson's pass and fed Gervin for a fast-break dunk that cut the Los Angeles lead to 69-61.

A reverse layup by Johnny Moore got the Spurs to 72-65, but Magic Johnson made one of two free throws and Nixon fed Michael Cooper for a spectacular lob dunk. After Mark missed, Abdul-Jabbar made a thunderous dunk off a feed from Nixon and the Laker lead was 7765.

Fast breaks by McAdoo and Cooper soon had the Lakers back on top by 16 again. The Spurs wouldn't wilt, thousgh, and outscored the Lakers, 8-2, at the end of the quarter to cut the margin to 89-79 going into the final 12 minutes.