"Hands Across the City," the District school system's ambitious demonstration of support for education, could have used a few extra hands yesterday.

The plan was for civil defense sirens to sound at 11:25 a.m. Police would then halt traffic on 35 miles of city streets and 250,000 schoolchildren and government workers would step off the sidewalks, hold hands and sing a song composed to celebrate American Education Week.

But months of planning went awry. Along large portions of the route, there was no sign of the human chain. Traffic kept flowing. Most principals kept students on the sidewalks. Through much of the city, participants couldn't hear the sirens. School officials said radio station WHUR-FM did not play the song children were to sing; the station instead played a spoken version of the lyrics because the tape provided by the school system was not clear enough to play on the air, said WHUR's Karen Campbell.

By the school system's estimate, the turnout was -- at best -- one-third of the anticipated number.

School administrators had promised to bring the city to a momentary standstill to send a strong message of public support for education. They got permits from District police, Capitol police, the White House and the Office of Emergency Preparedness. They enlisted help from 650 police officers, planners from the fire department and dozens of city and federal agencies that have adopted D.C. schools.

But streets stretching across the city and through all eight wards were dotted with only occasional groups of students and most roads teemed with the usual stream of groaning buses, chugging trucks and honking taxis.

"I don't know what happened," said school system spokeswoman Cheryl Johnson. "I can only stress how pleased we were to see 500 people lined up on Pennsylvania Avenue." Those people were several hundred workers from school system headquarters at 12th and Pennsylvania NW, joined by Mayor Marion Barry and several D.C. Council members in front of the District Building.

No children could be seen along five blocks of the main route downtown. Nor along M Street in Georgetown. Nor up most of Wisconsin Avenue to the Montgomery County border.

Students who were to arrive by bus to join the mayor downtown didn't. Johnson said she didn't know why. "Some principals opted to have their children ring their schools instead of going over to the chain," she said. "I guess we should have had specific commitments from government agencies and the schools that they would be participating."

Principals said many students, who had made D.C. public school flags in art classes and rehearsed the song at assemblies, did join hands.

"My kids went out on Maryland Avenue and they enjoyed it immensely," said LeGrande Baldwin, principal at Maury Elementary School at 13th Street and Constitution Avenue NE. Students from Deal Junior High School in upper Northwest lined Nebraska Avenue and sang along with the tune pumped out on boom boxes.

"People waved to us from their yards as we went by," said Thomas Kelly, principal at J.F. Cook-Slater-Langston Elementary Schools at P and North Capitol streets NW. "It raised the consciousness of the people."

Richard Robinson and 13 other University of the District of Columbia students walked to the District Building from the Mount Vernon campus for what they thought would be a massive demonstration. They were ready to sing the song, "Embracing the City." But no one around them did. "I guess we needed a piano," Robinson said.

To make up for the logistical breakdown, TV reporters anxious for lively footage tried to persuade Barry, school board President R. David Hall (Ward 2) and three council members to form an impromptu quintet and sing the education song.

"I'm an excellent singer," the mayor said. But the politicians couldn't figure out the tune in time and after a few moments, the cameramen wandered off. There would be no concert. "This just goes to show you, politicians don't say they can do everything," said D.C. Council Chairman David A. Clarke.

Barry said he joined the chain "to emphasize the need for quality public education. We're making great strides at our elementary and junior high school levels. We have some ways to go at our high school level because of drugs and the problems that all urban centers face."

When the sirens sounded faintly, "the police didn't hear it and a lot of people didn't hear it, and no one stopped the traffic," Johnson said.

While he waited for someone to move the crowd into the street to sing, David Junious, a school system worker, waved miniature American and D.C. public school flags. "This will bring people together," he said. "Our exuberance will carry over to get people excited about education." Twenty minutes later, as the crowd dispersed without having sung or set foot in the street, Junious wondered, "What happened? We expected more people."

David Salie and Kristen Donoghue, 19-year-old Georgetown University students, arrived at Wisconsin Avenue and M Street hoping to find a place in the human chain. They found the usual midday traffic. "I wasn't in the country for Hands Across America," Salie said. "I would think on Wisconsin it would be busy. We figured public schools were a good cause."

Johnson declared the event a success "despite the snafus." But she added that "I doubt we would try again anytime soon. I think it's a one-time event."

Staff writer Lynne Duke contributed to this report.