The San Diego Charger Trademark was designed when Dan Fouts was a young 49er fan growing up in San Francisco and Don Coryell was devising the system that would establish him as one of football's foremost pass masters.

Nineteen years later, these two have blended talents to personify the lightning bolt that adorns the helmets and jerseys of the team that currently rules as best in the National Football League's AFC West.

When the Chargers square off against hated Oakland here Thursday (WJLA-TV-7, 9 p.m.), Fouts will be seeking to become the first player in modern professional football to pass for more than 300 yards in four consecutive games.

His 326-yard performance against Los Angeles Sunday, following 305-yard and 318-yard games against Denver and Seattle, respectively, made him one of only seven players to reach the 300-yard plateau for three games in a row.

Fouts was the third-ranked passer in the NFL last year, behind the two Super Bowl quarterbacks, Pittsburgh's Terry Bradshaw and Dallas' Roger Staubach, but he really seems to have reached full flower in his first full season under Coryell. The secret would seem to be Coryell's emphasis on the pass and the "tree system" he employs in tracing receivers' routes.

Coryell, who sent a steady stream of quarterbacks and receivers into the pros during 12 years as head coach at San Diego State before moving on to the St. Louis Cardinals, took the Charger helm from Tommy Prothro four games into the 1978 season. However, he did not plant his "tree until this year.

Simply stated, the Coryell system, which he worked out while coaching at Whittier College in the late '50s, provides for a few basic routes, with specified limbs branching off from the trunk. Each route is numbered, so any receiver, then, can run a "1" or a "4" or a "9" and play calling is as simple.

It then becomes a matter of Fouts reading the defense, deducing which receiver should be open and getting the ball to him. Fouts has expertise in each of these areas.

"He has an uncanny abiltiy to read defenses," said Ray Perkins, former San Diego offensive coordinator, now head coach of the New York Giants.

Another former offensive coordinator of the Chargers, San Francisco 49er Coach Bill Walsh, describes Fouts "the best leader I've seen."

To tight end Bob Klein, Fouts is "probably more confident than any quarterback I've ever played with."

Coryell won't argue with any of those assessments. "Fouts is very intelligent," he said, "very calm and composed . . . a courageous-type man, who will stand in there under pressure. He does an excellent job of getting the ball to someone who's open.

"He doesn't do it every time, nobody does."

He does it more frequently than anbody else. His 64 percent completion average is best in the NFL, and his 1,940 yard passing also lead the league. He has thrown only nine interceptions.

Although Fouts hopes to get the ball to one of his deep threats, pro sophomore John Jefferson or old pro Charlie Joiner, he has employed 11 different receivers, and seven are in double figures.

"Everbody's getting involved," Joiner said. "It has to be a team thing.

"Dan don't pick no receiver," he added, laughing."He goes to the person who's open. He has confidence in all of his receivers."

Jefferson, who played in the Pro Bowl as a rookie last year when he tied a league record of 13 touchdown catches by a first-year receiver, has 31 receptions for 522 yards, and Joiner, whose 11th season is proving to be one of his best, has 26 for 434 yards.

Although Fouts definitely is The Man in the Charger success story (they lead their division by a game as they head into the second half of the season), he would prefer to downplay his achievements.

"Football is a team game," he said. "the satisfaction comes in winning, and that's not an individual thing.

"When you get the time to throw (he has been sacked 11 times in eight games) and your receivers are open, it's not difficult to complete a pass."

He also insists that opposing defenses dictate the Charger bombs-away approach. "We take what they give us," he said, indicating that the opposition is more geared to stop the ground game than the aerial attack.

This is just a team that does what it has to do," he said.

Coryell agreed with his field general. "We'd much rather hand off the ball to a back and let him run," he said. "We don't care how we get yards and touchdowns as long as we get them. If we have the opportunity to get them on the ground, we'll take 'em. It's much safer.

"But," he concluded, "we'll do what we can do best."

And that's fill the air with footballs.

"Awesome is a good word for them," said Oakland defensive end Pat Toomay. "It's their offensive philosophy. Fouts uses everything. He dinks here and dinks there; meanwhile, Jefferson is screaming down the sideline.

"It's difficult to get to Fouts," he added, "and he always has a safety valve to go to."