As 23 of 28 National Football League teams prepare to open training camp this week, the league apparently is going to lose St. Louis running back Stump Mitchell to the U.S. Football League.

Mitchell, a part-time starter with the Cardinals, has agreed to a three-year, $1.5-million deal with the Arizona Outlaws, according to published reports in St. Louis.

Mitchell is expected to sign soon in Phoenix.

"I'm an Outlaw now," Mitchell told United Press International. "I hope everybody knows how much I wanted to stay with the Cardinals. I'm going to miss playing with talents like Roy Green and Ottis Anderson, working with Neil Lomax, playing for a coach like Gene Stallings. But I couldn't turn this down."

Harold Lewis, Mitchell's agent, said the deal was not completed. "The door isn't closed entirely," Lewis said. "We've tried everything possible to keep Stump in St. Louis. We tried harder than anything we ever tried before. And we'd still be willing to try."

Mitchell, a ninth-round draft choice from The Citadel in 1981, has rushed for 2,177 yards in five NFL seasons.

The Cardinals are one of four NFC East teams scheduled to open camp this week. (The Dallas Cowboys began practicing last week because they play a preseason game against Chicago in London next month.)

The Washington Redskins will open camp Monday (July 21). Rookies and selected veterans are expected Sunday for physicals. The Redskins train at Dickinson College in Carlisle, Pa.

The Super Bowl-champion Chicago Bears also start practice this week in Platteville, Wis. Maintenance workers there bolted two dormitory beds together to accommodate lineman William (The Refrigerator) Perry.