Yesterday was the first day of the 1978 Hispanic American Festival in Adams-Morgan, and the first event was devoted to the art of children - trying to convey in pictures a heritage that many know only second-hand.

While some adults celebrated, as well, with soccer and football games in a park near far-off Wisconsin Avenue, more than a hundred parents and grandparents brought their children to tha basement auditorium of Sacred Heart Church on 16th Street and Park Road NW.

"What we try to do is get together all the Hispanic people," said festival president Marcela Davila. "You know there are 23 countries here in the area, and the main thing is to gather the people and have a reminding of their home countries."

In the childrens' art there was much "reminding," both in the colorful style and the images of Latin life: a brown cathedral with a glowing white cross broadly brushed in tempera; a brilliant orange whale floating on a sea of rippling green and purple, blue and red; a second-grader's angel with dark orange skin and flowing blond hair, a dress with flowers on it like pinwheels, all set against a hot pink sky.

Seeking images of their countries, some children drew tiny houses with thatched roofs and bright green mountains behind them. Fifth-grader Gary Dixon, from Trinidad, painted a startling white Holiday Inn surrounded by palm trees.

"We like to have involved the kids," said Herlinda Guerra, an art specialist with the D.C. Department of Recreation who organized the show. "They are Americans now, but look, you can see they have a tradition. We ask that they put in the most of their countries."

The exhibit of children's art ends this afternoon, but there will be many more activities during the week.

Wednesday there will be an open bazaar for senior citizens and a picnic at Fort Hunt for Hispanic children. That night there will be a family hour at the new Marie Reed Community Learning Centr at Champlain Street and Kalorama Road NW.

Thursday will be devoted to Hispanic women, combining entertainment with workshops on nutrition, employment, immigration, housing and health problems.

Saturday there will be cultural presentations - drama, poetry and music - and on Sunday the festival will be capped off with the "Gran Desfile Hispanoamericano," a parade ending at Kalorama Park.