Crime reports in Montgomery County increased 4.1 percent last year over 1983, running counter to national and local trends in a surge that was expected but still troubling, county police said yesterday.

"Any crime increase is a concern," Police Chief Bernard D. Crooke said yesterday. But he noted the rate was still well below the all-time high recorded in 1980. "Since 1974, it's the third-lowest crime rate that we've had. So it's nothing for everybody to go out and buy a bullet-proof vest."

Crimes against people increased by 6.2 percent, while property crimes increased by 4 percent. Murder, robbery and school burglaries were the only categories to show reductions. Rape reports increased by 10.5 percent, burglaries by 2 percent and car theft by 15.9 percent.

Last year, when announcing decreased crime figures, Crooke said he believed the crime drop was temporary and was "going to go back up." Yesterday he said that "historically, crime has peaks and valleys," while the causes of such changes remain far less certain.

Crooke said a 6.5 percent increase in the number of juveniles arrested and a 67.2 percent increase in the number of child-abuse cases reported were two areas of particular concern.

Last year, 3,213 juveniles were arrested for criminal offenses, he said, more than 30 percent of the total number of arrests made by county police. "It's quite a problem," he said. Although he said there are no obvious answers, Crooke complained that the resources of the court system are too heavily weighted in favor of adult criminals.

Although twice as many adults as juveniles are arrested, Crooke said the resources are even more skewed toward adult offenders, with the emphasis on the adult courts "way out of line." There are 19 judges, for instance, serving in the county's adult courts while two are assigned to juvenile matters.

Crooke said he hopes to increase the number of officers working with child-abuse cases. Police said 296 child-abuse cases were reported last year, compared with 177 in 1983.

Sgt. Ingrid McKee of the police Juvenile Division said sex-abuse cases accounted for almost all of this increase and make up about 40 percent of the child-abuse cases reported. "The sexual abuse increase has been phenomenal, absolutely phenomenal," she said.

McKee and county child welfare officials agreed that the increase was probably due largely to increased reporting and improved investigation. Mary Lou Hurney of the county's Department of Social Services, which investigates these crimes together with police, said, "The more attention that is brought to this subject, the more cases will be brought to light."