County Administrator Shot; Ex-Worker Held : Violence: A former social worker surrenders to deputies. The victim, who took part in the suspect’s firing, is in serious condition.

A Los Angeles County social worker who was fired from her job in Santa Fe Springs a year ago walked into her former office and shot a supervisor who participated in the decision to let her go, officials said Tuesday.

The assailant, identified by deputies as Wanda Rogers, 43, surrendered about at hour later at a San Bernardino County sheriff’s station in Chino Hills, investigators said.

The victim, Thu Nguyen, 53, was flown by helicopter to the Martin Luther King Jr./Drew Medical Center, where he was reported in serious but stable condition after treatment for a gunshot wound to the mouth.

Schuyler Sprowles, a spokesman for the Los Angeles County Department of Children’s Services, said Rogers had been employed as a social worker, handling cases involving child abuse, foster care and adoption, from 1989 until she was fired in February, 1992.

“Obviously, the termination has something to do with her performance, but I can’t go into specifics,” Sprowles said.

Nguyen, one of several supervisors at the Santa Fe Springs office, has worked there since 1978, Sprowles said.

Witnesses said Rogers entered the department’s regional headquarters at 10355 Slusher Drive about 12:30 p.m. Tuesday, walked past a group of people celebrating a baby shower with balloons and other decorations and into the cubicle where Nguyen was sitting.

According to investigators, the woman fired a single pistol shot at Nguyen at close range.

“We heard the pop, but we thought it was a balloon popping,” said Florence E. Schuchman, an office employee.

Sgt. Robert Stoneman, a spokesman for the Los Angeles County Sheriff’s Department, said that as the severely wounded victim collapsed at his desk, Rogers ran from the building, got into her car and drove away.

About 1:40 p.m., Rogers surrendered to deputies at the San Bernardino County sheriff’s station. Officers there said a pistol believed to have been used in the attack was taken from Rogers when she surrendered.

Several department employees said that security is inadequate. Judy Hammond, a department spokeswoman, said that because the public seldom visits the building--used primarily for paperwork--security is not as tight as at the department’s field offices.