It felt like a day at the circus. Under sunny skies, turquoise balloons and red-striped canopies, soul singer Stacy Lattisaw, the Marine Band and Nancy Reagan greeted about 2,300 schoolchildren at the White House. The children, dressed in green "Just Say No" T-shirts, had walked to the south lawn from the District Building as part of a series of antidrug marches across the country from Birmingham, Ala., to the Rose Bowl in Pasadena, Calif.

While the children waited for the first lady to appear, some pondered questions about drug use.

"You can basically see people dealing drugs in the school," said Suitland High School student Kevin Emory, 16. Of his class, "I guess about five or six use drugs."

"I see 'em smoking it on 14th Street," said West Elementary School student Domingo Stevenson, 12, who has to walk that way every day to get to his 13th Street home.

"There's a guy called Cooter," said Monique Parrish, 12. "He be selling drugs on 14th Street . . . He asked my sister did she want drugs. And she said no."

Monique's sister had done just what Mrs. Reagan asked in 1984. When the first lady visited a school in Oakland that year, a student asked her what to do if propositioned for drugs. Mrs. Reagan's reply was "Just say no." The students formed the first Just Say No club in January last year, and an estimated 5,000 such clubs have proliferated since across the country.

Mrs. Reagan's interest in the issue has also been picked up in the Senate and internationally. Sen. Paula Hawkins (R-Fla.) recently introduced a resolution to establish an annual Just Say No Week. No clubs have since been established in Brazil, Great Britain, Jamaica and Sweden, according to the White House. Yesterday's event, in fact, was labeled the first Just Say No International Walk.

When Mrs. Reagan appeared, the crowd hum was temporarily interrupted by a throaty cheer.

"There are groups as big as yours, or even bigger, doing the same thing all over the world," she told the chattering children. "Children everywhere are learning about drug abuse at an early age." It was the introduction to a call-and-answer session for which WYKS-FM deejay and emcee Donnie Simpson had rehearsed the young crowd.

"What should you do when someone offers you drugs?" asked Mrs. Reagan.

"JUST SAY NO!" was the reply.

"And what WILL you do when someone offers you drugs?"

"JUST SAY NO!"

"I can't hear you!" cajoled the first lady, reading from her script.

At that, the children screamed the slogan with an enthusiasm not often seen until after graduation and, as rehearsed, let their balloons fly skyward in a cluster of turquoise hope for the television cameras.