Montgomery County Police Chief Donald E. Brooks yesterday ordered an investigation into a charge that an off-duty county police officer beat a man at a shopping center Monday night. One witness said the man "was battered around like a rag doll."

Brooks said he initiated the probe "in the best interests of the department, even though a formal complaint had not been filed." Brooks declined to identify the officer allegedly involved in the incident until a brutality complaint is received by the department's Internal Affairs Office.

The department is barred by state law from taking disciplinary action against a police officer unless a brutality complaint is filed within 90 days of the alleged incident, a police spokesman said.

Yesterday, Danny M. Callihan, who witnessed the incident, said he intends to file a complaint next week. The victim, a 30-year-old man known only by the first name Jose, has declined to file a complaint, police and Callihan said.

The alleged beating occurred around 10:30 p.m. Monday in the parking lot of a shopping center at Veirs Mill and Randolph roads in Wheaton. Some of the center's store owners say they have complained to police of loitering and drug dealing in the parking lot.

Callihan, an elevator repairman, said a man dressed in a T-shirt and slacks flashed a badge and confronted him and two other men while they were standing outside a pizza parlor at the shopping center. Callihan said the man, who was driving a red pickup truck, asked the three men whether they had been in the drugstore.

Callihan said the man then grabbed and began beating one of the men with his hands and the butt of a handgun. "He hit him several times with his arm and forearm. He had the gun in his face . . . all the blows were to his head. The guy's shirt was twisted in one hand."

Callihan said the victim's face was severely swollen from the beating. County police took photographs of the victim, who refused medical assistance, police and Callihan said.

"It was something else," Callihan said. "This officer was screaming at him the whole time. It didn't make sense. I've never seen an officer act like that before." Callihan said the man sped away after the beating.

Walter Bader, president of the county's Fraternal Order of Police Lodge 35, disputed some of Callihan's claims. "The injuries were not as serious as alleged," Bader said. "This officer was responding to a serious assault against his wife."

Bader said the officer's wife, who does not know the alleged victim, was assaulted while leaving the drugstore earlier that evening. "Police officers are people," Bader said. "We don't hold our families to any lesser degree of protection because we're police officers. Our families come ahead of the badge."