Drug-related arrests of Montgomery County juveniles the first four months of this year were only about half what they were for the same period last year, but citations for alcohol violations increased by more than a third.

Montgomery police said yesterday that the number of drug charges lodged against juveniles dropped from 84 during the first four months last year to 41 this year, a decrease in the rate of arrests from about 20 a month to about 10 a month.

At the same time, police said the number of juveniles cited for alcohol violations increased from 90 during the first four months of 1982 year to 144 this year.

County school officials, who included some of the figures in a report that will be delivered to the Board of Education Monday, reacted with caution.

A recent state-wide survey indicated that drug use among high school students had declined slightly over the past two years, but that those students using drugs were using a wider variety. In the same survey, it was reported that drug use among eighth-grade students had increased slightly.

"Just because there is a drop in the reports does not mean kids are not taking drugs," said Richard Towers, director of the school system's department of interagency, alternative and suplementary programs, who prepared the report for the board. "Kids may be just getting smarter about where they do it."

The survey conducted by the Maryland Drug Abuse Administration reported that 29 percent of Montgomery County seniors and 19 percent of 10th graders said they used drugs during 1982. Seventeen percent of the county's eighth graders said they had used marijuana during the year.

In the report that will be given to the board next week, Towers says that the the number of suspensions for drug use through May dropped significantly. Suspensions for using alcohol showed a somewhat less significant decline that some school officials say may be erased with the tabulation of figures for June, a month marked by end-of-school celebrations.

From September through May, 144 students were suspended for using drugs, a rate of 16 a month. During the entire 10-month school period last year, 191 students were suspended for using them, a rate of more than 19 a month. During the first nine months of the latest school year, 126 students were suspended for drinking alcohol. Last year during the 10-month period, 149 students were.

School officials did not have the figures broken down between junior and senior high schools, but Andrews says in the report that despite the overall decline the reported increase in drug use among eighth graders should dictate increased efforts for preventing drug use by elementary school students.