U.S. Park Police have begun a crackdown on teen-age drinking in federal parks around Washington - particularly Fort hunt, Carderock and the two Great Falls parks - where large flocks of high school students have been gathering on "skip days" and weekends.

Signs announcing that alchollic beverages are prohibited in the parks were posted last week at both the Virginia and Maryland Great Falls parks and at Carderock, all operated by the National Park Service. The signs were first put up over a month ago at Fort Hunt, near Mount Vernon, where U.S. Park Police had been arresting more than 100 teenagers a weekend on charges of drinking in public.

There were beer busts at Great Falls and Carderock both last Friday and Friday, March 18 - two "skip days" when an unofficial exodus depleted many area high schools and hundreds of cars loaded with teen-agers and beer converged around Great Falls.

The scenes at the parks, which resemble Fort Lauderdale, Fla., beaches each spring when vacationing college students swarm to the water's edge, generally have been peaceful with the major activities frisbee throwing and getting a sun tan. MMany students had beer but there was little public drunkenness.

But the Park Service has become concerned about drinking liquor at Great Falls, where the rocks and torrents of water have made the scenicspot one of the nation's most dangerous federal parks. Last year 7 persons were killed around the falls, the average number of deaths there each year now for almost a decade.

"While we welcome teen-agers, like everyone else, to our parks, we also are concerned when they block park roads and parking lots and deter families from visiting the parks," said Mary Krug, spokeswoman for the Park Service's national capital region. "But our major concern is over the danger of drinking is prohibited in all federal parks here except at marina snack bars that serve beer, at special events like parades and the Folklife Festival and in sections of parks when parties get special permits to serve alcoholic beverages. Both Fort Hunt and Carderock have pavillions where parties can obtain such permits.

On Friday, cars entering Carderock were stopped by Park Police, drivers asked for identification and whether they had beer or other alcoholic beverages in their cars. Large quantities of beer were confiscated and 12 youths given citations for drinking in public. The citations, fines of $10 for juveniles and $50 for those 18 and over, constitute an arrest record for drinking in public, according to U.S. Park Police. At least 50 citations also were given youths at both the Virginia and Maryland Great Falls parks on March 18.

Several area police forces have become concerned about public drinking because crowds of 100 or more persons drinking are considered threatening and a nuisance to others. They are also, police said, difficult to break up without incident.

While much of the public drinking by teen-agers has been on weekends, the phenomenon of "skip day" has expanded the party problem into the week as well.

Skip days have been popular at many area high schools for half a dozen years. "The tradition for seniors is, say, in 1976 to take off the 76th day of the school year," says Fairfax High School principal Clarence Drayer.

"The 77th day for the class of 1977 was March 18 and we had a lot of kids out of school that day . . . But let's face it, there's a high degree of absenteeism on Mondays and Friday's both in the U.S. government and in private industry," says Drayer. "We don't recognize skip day but many parents condone it and write excuses for their kids to be out of school and then many 18-year-old seniors can sign themselves out as adults if they fill out certain forms."

Robert Russell, principal of Fairfax's Robinson Secondary School, says, "We're all aware when a skip day's coming but we combat it in different ways. We had a large absence, as much as 80 per cent of the senior class gone at some point during the day (March 18th), but while we told them there would be business as usual at school we also said we would view any absences with some understanding even without a note from home.

"We're concerned about it spreading and about alcohol but the senior skip day is completely innocent. They're soon to graduate and they're spreading their wings."

On the rocks at Great Falls last Friday, sunning herself and relaxing on the last day before spring vacation, one of a half dozen Montgomery County seniors said, "It was a beautiful day and we just took off when we heard everyone else was. It's the only day I've missed school this year. I don't feel guilty."