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

Signs announcing that alcoholic 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 teen-agers 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 resembled Fort Lauderdale, Fla., beaches each spring when vacationing college students swarm to the water's edge, generally have been peaceful with the major activity frisbie throwing and getting a sun tan. Many students had beer but there was little public drunkenness.

But the Park Service has become concerned about drinking liquor in the parks and at Great Falls especially, where the rocks and torrents of water have made the scenic spot 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," says Mary Krug, spokeswoman for the Park Service's national capital region. "But our major concern is the danger of drinking on the edge of a precipice."

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 get 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 days" 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 out of school that day. . . . But let's face it there's a high degree of absenteeism on Mondays and Fridays both in the U.S. government and in private industry," says Drayer.

Many of the hundreds of youths at Maryland's Great Falls park on Friday were from Wheaton High School, where assistant principal Ann Meyer estimated as many as 50 per cent of the 600 seniors had disappeared that day.

"In some classes there were only 3 students instead of 18 to 25. There was nothing like this last year," said Meyer. "We heard that local disc jockeys were announcing a skip day that day on the radio. It's contagious and it seems to be a growing tradition among seniors here at other schools. The local school systems are going to want to take a look at the problem . . . which could be very stressful for police if they're all going to one or two parks."

Private schools also have been affected and have various attitudes toward skip days.

At Elizabeth Seton, the Catholic High School for girls in Bladensburg, about 50 per cent of the senior class of 184 observed skip day as a holiday on Thursday, March 17, because Friday the 18th was a school administrative day, said principal Sister Vincentia. "I'd planned it that way last fall because I knew the 18th would be a skip day and they would be off . . . but evidently that wasn't enough."

Many Elizabeth Seton seniors had parental permission for their absences "and in that case there's nothing we can do even if we don't go along with that philosophy," said Sister Vincentia.

At DeMatha High School, the nearby Catholic school for boys in Hyattsville, principal John Moylan said his school endorses skip day as a senior privilege.

"They get few privileges in four years of high school and it's a minor concession. There's no harm in it and it's a good morale booster," he said.

On the rocks at Great Falls last Friday, sunning herself and relaxing on the last day before spring vacation, one of a group of Wheaton High School 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."