Sarah Blumsach, 4 slopped waterbased paint on a long sheet of paper - dribbling some on her dress in the process - and then stood back. It was, she declared, a picture of "a big blob."

Within the next half-hour, Sarah had gleefully swatted her father with a styrofoam sword in a playful game called "boffing," painted a laughing teen-ager's face with yellow and black grease paint, and had her own face painted like a clown's with a huge red mouth stretching practically from ear to ear.

It was all part of the festivities at the first free Sunday afternoon festival of the year at Glen Echo Park where people of all ages now will be able to dabble in art, poetry, listen to music, learn about gardening, watchmime as well as other cultural activities.

"I tell as many people about this place as I can," said Marty Blumsach, Sarah's father and a program analyst for the National Institutes of Health, has great potential. There is a sense of community here."

Yesterday must have been much like those sultry summer days that attracted people to Glen Echo in the 1890s when the "Chautauqua movement" flourished. That movement combined the arts with education and recreation, and yesterday the festival's organizers showed how they hoped to meld the idea to modern tastes.

"I think it's terrific," said Ann Ridge, an American University arts administration student who supervised the "paint-in," a free-for-all for budding artists."More than that, I think it's important. Families don't have enough time to spend together and don't have enough places they can go and enjoy together."

After its Chaatauqua days, Glen Echo, nestled between MacArthur Boulevard and the Potomac River over the C&O Canal in Montgomery County, became the site of vaudeville shows and later, during its best-known incarnation, an amusement park.

There, the giant "Coaster Dip" sped up to 86 miles per hour and the "Swing Era" brought famous musicians like the Dorsey brothers to the renowned Spanish Ballroom with a dance floor park authorities claim was unmatched in the area.

The amusement park eventually closed in 1968 and for a time resembled a great white elephant. Ignored, its rides and amusements were removed and sold.But the National Park Service acquired the shabby and deserted property in 1971 and decided to open the park to a number of imaginative proposals.

Glen Echo now houses 25 resident artists who teach more than 150 courses, the 25-year-old Adventure Theater for children and a children's experimental arts day camp. The Park Service is seeking a $340,000 appropriation from Congress that would make the dilapidated buildings safer, do minimal refurbishing of peeling paint and saggin roofs, and add heat for year-round use.

Onc can still visit Glen Echo on a Sunday and take a 25-cent ride on the 1922 carousel with its 55 handcarved horses, rabbits, deer and lions, whirling round and round for five minutes to lilting calliope music.

The view from the carousel takes in the empty Crystal Pool, its musty locker room and filter plant converted into a sculpture studio; a children's playground of rubber tubes and tree trunks, the "art deco" ballroom where people can, for $2 per person, dance to country, folk and square dance music every Saturday night, the Writer's Center with classes and publishing equipment and studies for woodworking pottery and fiber arts.

"We don't teach esthetics, we nurture them. I have students from housewives to surgeons," said potter Lloyd Lackey, one of resident artists.

Program director Bev Chapman explained the park's concept as one that encourages people "to devote their leisure time to artistic creativity . . . which we believe each person possesses."

Apparently the participants yesterday caught on.

A toddler who walked by the "paint-in" was told by his mother that he was "too little to paint." A man looked at her and retorted, "Were you ever too little to paint?"