The number of students caught using drugs or alcohol in Montgomery County public schools has dropped dramatically since officials began enforcing tough antidrug regulations four years ago, according to school records.

School officials hope that the statistics, which show more than a 50 percent drop over the four years, mean that fewer students are using drugs and alcohol. But they cautioned that the figures only measured the number of students caught using drugs or alcohol on school grounds.

"There is no doubt that there is less drug use in the schools, but there is no way to tell if drugs are being used less frequently overall," said Deputy Superintendent Harry Pitt.

In the 1978-79 school year, 516 high school students were caught using drugs or alcohol on or near school grounds, a large number of them due to a special police surveillance of the schools in the fall. Last year, following a consistent three-year decline, there were 169 students caught in the county's 22 regular high schools and three special high schools.

The only other metropolitan area reporting a similar decline is Prince George's County, where officials say 632 secondary students were caught last year compared with 802 secondary students four years ago.

In Fairfax, the number of arrests remained almost constant between 1978-79 and 1980-81 (officials didn't have figures compiled for last year). Four years ago, 858 students were suspended for drinking or taking drugs; in 1980-81, the number was 857.

In the District, school officials pointed out that statistics have been compiled only since last year and are incomplete. Only 10 drug-related incidents were reported last year and none has been reported this year, officials said.

In Arlington, where there are three public high schools, 10 students were caught using drugs in 1981-82, up from three the previous year. Officials didn't have figures before 1980.

Montgomery school official Kenneth Muir said the use of hall monitors in every high school and stepped-up enforcement of regulations are responsible for much of the decline in that county.

Enforcement tightened up as a result of 1978 raids that were designed to catch drug dealers. At the time, the school system came under intense public scrutiny, with parents calling for stricter enforcement of existing regulations. As a result, school officials began to put into effect automatic five-day suspensions on first offense, a policy that had previously been ignored. Officials also began notifying police of every violation.

During the first two months of this school year, 23 senior high school students have been arrested for using drugs or alcohol in Montgomery. County school officials said they plan to continue rigorous enforcement of drug violators.