VIRGINIA BEACH, JULY 17 -- A Circuit Court jury convicted a mother of involuntary manslaughter and three other charges today in the beating death of her 13-year-old adopted son and recommended she serve 31 years in prison.

The jury deliberated 10 hours over two days in the trial of Karen Diehl, 36. Her husband, Michael Diehl, 42, was convicted by a separate jury Wednesday of first-degree murder, abduction, felony child neglect and misdemeanor assault. The jury recommended that he serve 41 years in prison and pay a $1,000 fine.

The Diehls, fundamentalist Christians who believe in strict discipline, were tried on charges arising from the Oct. 29 death of Dominick J. (Andrew) Diehl.

Karen Diehl had been charged with murder, but the jury convicted her of the lesser manslaughter charge and recommended the maximum sentence of 10 years. She also was convicted of abduction and felony child neglect with a recommended sentence of 10 years on each charge. She had been charged with malicious wounding, but the jury opted for a lesser charge of misdemeanor assault and recommended a 12-month term.

Circuit Judge Alan E. Rosenblatt set sentencing for Sept. 16 and allowed her to remain free on $45,000 bond.

Thomas B. Shuttleworth, Karen Diehl's attorney, later told reporters that she was happy. "We weren't going for the big 'not guilty,' " Shuttleworth said. But he said he will appeal the conviction on the abduction charge.

Commonwealth's Attorney Paul C. Sciortino said the jury apparently decided that Karen Diehl acted without malice. "I think justice was still served," he said.

The prosecution had contended that Karen Diehl had inflicted the fatal blows to her son's head.

The couple and their 17 children left their Post Falls, Idaho, home in 1984 for a camping trip around the country. They arrived at a Virginia Beach campground in spring 1986.