To determine what is wrong with the San Diego Chargers, it is necessary to know what the Chargers are. They are electric.

The lightning bolt that zig-zags across their blue headgears is a fitting symbol for the Chargers, who can light up the skies on offense.

If their defense hasn't been much, no matter; the offense simply would outscore the other side. A simple enough equation.

Only this season, it hasn't worked, and there doesn't seem to be any single reason why the Chargers stand at 3-5 halfway through the National Football League's 64th season.

This is a San Diego team that at the season's beginning was among the favorites to win the Super Bowl. Only Dallas was a shorter price.

The Chargers came into the season with optimism. They had been husbanding their draft choices for 1983, when the athletes available were considered of surpassing quality. They had two picks in the first round, two in the second. They would use them to buttress their defense.

The offense was still directed by quarterback Dan Fouts, at 32 at the height of his considerable skills. Fouts began the summer comforted by a new, six-year contract that reportedly will bring him $7.2 million. And he was surrounded by Chuck Muncie, James Brooks, Wes Chandler, Charlie Joiner, Kellen Winslow--all marvelous athletes.

But things started souring even before training camp. One of the second-round draft choices, running back Gary Anderson of Arkansas, defected to the U.S. Football League, and there was another, not so little problem, named Louie Kelcher. The team's likely defensive noseman reported at a fat 345.

There were more problems created by the shift of Pro Bowler Gary Johnson from tackle to end, where he has not been as effective. And top draft pick Billy Ray Smith, whom Coach Don Coryell had described as "a going concern," was no more than adequate as a linebacker.

A fractured ankle to free safety Tim Fox also has been damaging, but Fox should be fit for Monday evening's game here against Washington.

The Chargers, in sum, have not improved defensively.

Offensively, the Chargers still are state of the art when they are healthy. But, though they have scored on almost a point-a-minute pace, they too seldom have had the football. They have scored 25 touchdowns, their opponents 28.

Still, with a bit more luck, the Chargers easily could be 6-2.

Against Cleveland, they were in a position to run out the clock on what would have been a 24-21 victory when Fouts completed a pass to Winslow. But Winslow was cited for offensive pass interference, a ruling the NFL's director of officials, Art McNally, later admitted was not based on fact. The Browns got the ball, kicked a field goal and won in the first series of an overtime, 30-24.

Against New England, San Diego led, 21-13, when first Brooks and then Fouts appeared to earn a first down inside the Patriots' one-yard line. When the ball was spotted--faultily, the Chargers contended--San Diego was short. At the end of the afternoon, it also was short on the scoreboard, 37-21.

Fouts has missed only one game, last week's 24-6 defeat in Denver, but he has been handicapped by a hairline fracture to his left wrist, a bruised right thumb, and a severely bruised right shoulder. Now the muscles in his shoulder also are strained. The club is loath to permit him to return, fearing if he does, he could develop a rotator cuff problem that could impair his career.

Behind Fouts, the Chargers offer a highly promising third-year quarterback named Ed Luther, but Luther doesn't have Fouts' insights.

Chandler, who caught for more than 1,000 yards in eight games a year ago, lost his preseason to a foot wound suffered in a minicamp, and he hasn't played back to his customary level. He's questionable for the Redskins game after suffering a bruised kidney Sunday.

To Coryell, there are no turning points. To him, football is too complex a game to be decided by a single play. No one thing has gone wrong. Everything has.