The number of suburban Maryland teen-agers who say they smoke marijuana declined by 37 to 54 percent in Prince George's County and by 24 to 36 percent in Montgomery County over the past four years, a survey released last week by state health officials indicated.

The officials said the decline mirrored a nationwide shift away from teen-age use of certain drugs.

The report noted that 29 percent of all Prince George's seniors at three high schools surveyed last fall said they had used marijuana at least once in the preceding month. Fifty-five percent of the seniors questioned at different schools in 1978 said they smoked it.

More than 3,000 students were given the 115-question survey, which they answered anonymously, at 13 different Montgomery County schools, and similar sharp declines in marijuana and other drug use were found.

The survey focused on the use of 12 types of drugs as well as alcohol and cigarettes by 8th, 10th and 12th graders.

In most categories, Prince George's and Montgomery students reported a slightly lower incidence of drug use than the statewide averages, which also declined over the past four years. But in one category, alcohol, the number of students reporting current and frequent use increased from 1978.

Eighty-four percent of Prince George's seniors at the three high schools were current users of alcohol, according to the study. A total of about 2,800 Prince George's students were questioned at three high schools and four middle schools. One in five of the seniors was a frequent alcohol user, reporting more than once a week or once a day drinking.

"Alcohol is still a problem," said Prince George's school spokesman Brian J. Porter. "Alcohol is going to be difficult to contend with as long as it remains a socially acceptable form of adult indulgence," he said.

"When you have 85 to 86 percent of seniors reporting having a drink in the last month, where can you go from there?" asked Richard Hamilton, who coordinated the study for the state. "We have a societal attitude that says to have a beer is okay," Hamilton said.

Use of the dangerous synthetic drug PCP in Prince George's has remained higher than the statewide averages and actually increased slightly over the last two years among Montgomery students, a cause of continued concern in both jurisdictions.

Seven percent of Prince George's seniors compared with 4.7 percent of seniors in Maryland as a whole report current use of the drug, which has been known to cause violent psychotic reactions in users.

Southern Maryland in general and Prince George's County in particular have been identified by federal drug officials as major centers of illegal PCP manufacture.

The number of eighth graders reporting current PCP use in Montgomery jumped from 2.8 percent in 1980 to 4 percent in 1982. In fact, Montgomery eighth graders reported slightly increased incidences of use in nearly all drug categories, despite the general trend away from drug use by students.

"We're starting this year on a very concentrated health program to reach down into the younger grades," said Richard L. Towers, director of Montgomery County schools Department of Interagency Alternatives and Supporting Programs.

Other results of the survey were:

* Nineteen percent of Prince George's eighth graders and 28 percent of seniors currently smoke cigarettes--about the same as Montgomery.

* Nearly 4 percent of eighth graders in Montgomery reported heroin use, compared with only 1.3 percent of the seniors there. State and local officials cautioned that because students did not have to sign their questionnaires, those statistics may have been inflated, especially among younger students.