President Carter's 9-year-old daughter, Amy, wearing blue denim pants and a white sweater, started classes yesterday at Stevens Elementary School. She is the first child of a President to attend public school in Washington in 71 years.

She arrived 12 minutes late and was accompanied by her mother and a detail of Secret Service agents. Their black Chevrolet had been delayed by the usual city phenomenon - morning rush-hour traffic.

"We just miscalculated how long it would take," Rosalynn Carter called out to reporters as Amy walked quickly up the front steps of the 108-year-old school, which was built for freed slaves and is now an island in a concentration of office buildings.

The refurbished building, with carpeted floors and bright, high-ceilinged rooms, is at 21st and K Streets NW, eight blocks from the White House, which lies within its attendance zone.

Of the school's 215 students, about 70 per cent are black, 10 per cent are American whites and the rest are Asian and Latin American. The children come from 20 countries. Many of their parents work for embassies - not as high-ranking diplomats, teachers said, but mostly in such jobs as clerks, drivers, cooks and gardeners.

Claudia Sanchez, the girl who sat next to Amy yesterday in fourth grade and showed her where to hang her coat, is the daughter of a cook at the Children Embassy.

"I don't talk too much, and Amy doesn't talk too much either." Claudia said after classes. "She's a nice girl."

As Amy arrived yesterday, the windows of buildings across the street from Stevens were lined with office workers and the reporters and photographers. Some children had trouble getting through to the school's front door.

But no visitors were allowed inside the school, and teachers and children said the day went normally.

"It was a pretty regular day," said Maurice Brown, a fourth grader. "There was a boy who kept going up to Amy a lot and asking if she wanted to draw. She said we could visit the White House sometime, but she didn't say when."

He said Amy read aloud to her reading group, did tumbling in gym class, and ate hot dogs and beans - the regular school lunch - in the cafeteria.

The class Amy is in has 24 students - 19 fourth-graders and five in the fifth grade. Her teacher, Verona Meeder, is the only white classroom teacher at Stevens. She has been at the school for 11 years.

Mrs. Carter remained at Stevens for about 15 minutes.

Amy stayed until 4:15 p.m., including one hour of after-school Spanish lessons, which she will take three days a week. Afterward, Mrs. Meeder came to the White House to give Amy a white puppy name "Grits," which was born on election night.

Until last week Amy had been attending the public elementary school in Plains, Ga., whose enrollment is about two-thirds black.

The last President to send a child to public school in Washington was Theodore Roosevelt, whose son, Quentin, was enrolled at the old Force School, on Massachusetts Avenue NW, from 1904 to 1906.