Jack Pardee, former head coach of the Washington Redskins, left pro football today to assume a marketing position with the Runnels Mud Co. of Lovington, N.M. Pardee, a native Texan, will work out of the Midland, Tex., office of the firm, a service company for drilling oil wells.

Pardee's resignation as associate head coach and defensive coordinator of the San Diego Chargers seemed to catch this city by surprise, as the team released a brief statement late in the day.

If it was a surprise, many Charger fans apparently considered it a welcome one. Although the Chargers reached the AFC title game against Cincinnati, they had the second-worst defensive record in the conference, and much of the blame was put on Pardee.

Pardee, 45, and twice NFL coach of the year, came here a year ago after three years at Washington, and with his reputation for defensive expertise, he was expected to help the Chargers into the Super Bowl.

However, as the Chargers yielded points generously, it was obvious something was wrong. While players complained that Pardee's system was too complicated, there were reports of dissension between Pardee and other defensive assistants.

Reached tonight at his home in nearby La Jolla, Pardee sidestepped questions about the Chargers' problems and instead chose to talk about his opportunity for advancement in the oil business.

"I've been in football a long time and I've enjoyed it and I'm sure I'm going to miss it," Pardee said. "But the time comes when you have to take a serious look at where you're going.

"The opportunity to become a head coach didn't come after this season, as I had hoped it would. I decided I had a better opportunity in another profession and this is the time to make the move and learn that business."

Pardee said he had been acquainted with the late Harold Runnels, a New Mexico congressman, during his stay in Washington. He was offered his new position by Runnels' widow, Dorothy, who is now running the company.

In Pardee's six years as a head coach, his teams compiled records of 42-46. His Chicago Bears team went to the playoffs in 1977.

"Obviously, we hate to lose a coach with the integrity, ability and courage of Jack Pardee," said Chargers owner Gene Klein. Coach Don Coryell, who hired Pardee, said: "We regret losing such a great coach and a great man. He is truly an outstanding coach and an inspiring leader."