White soldiers and police today rounded up hundreds of black children for not attending school, some under 10 years old, in a new crackdown that inflamed residents of this country's largest black community.

Hundreds of angry parents gathered outside the Moroka police station here this morning seeking word of missing children. By tonight, following the intervention of a group of clerics led by Anglican Bishop Desmond Tutu, most had been released, but an undetermined number of others faced the prospect of remaining in custody through the weekend.

Meanwhile, police confirmed that at least seven more persons have died in incidents of unrest, including six who were killed when police opened fire on a crowd in the small eastern Cape town of Aliwal North. The deaths, coupled with new outbreaks in black townships outside Cape Town, were further evidence that the government's nearly five-week-old state of emergency has yet to quell the political violence that has claimed more than 625 lives in the past year.

Authorities also announced the arrests of 17 more leaders of the United Democratic Front, the country's leading radical antiapartheid movement, 38 of whose leaders already have been charged with treason. The new arrests, made in Cape Town and Durban, appeared designed to forestall a march called by the front for next Wednesday on Pollsmoor Prison outside Cape Town to demand the release of jailed black nationalist leader Nelson Mandela.

The five front leaders arrested in Durban were identified as Dr. Farouk Meer, Billy Nair and Yunus Mohamed, who are classified as Asians, and blacks Noziswe Madlala and Themba Nxumalo.

Opposition sources said that the Rev. Allan Boesak, a leading dissident and front founder, failed to arrive at a speaking engagement near Cape Town tonight and could not be reached at home, Reuter reported from Johannesburg. They sources said that he could be in police detention but noted that some activists had gone into hiding.

The roundup of children in Soweto started yesterday with about 300 arrests of students caught outside school grounds by soldiers. Witnesses said some of the children were beaten with whips that are standard issue to soldiers and police. Most of them, including the youngest group, spent the night in jails, according to parents interviewed today.

The troops were enforcing new antiboycott regulations issued last week that make it a crime for students to be off school grounds during school hours. The rules, promulgated under the government's sweeping emergency decree, are an attempt to crush what has been one of the main weapons of young black activists seeking to demonstrate opposition to white minority rule and the government's apartheid system of segregation.

The white police commander for Soweto, Brigadier Jan Coetzee, was quoted in today's issue of The Sowetan newspaper as saying, "We are cracking down. We will not allow 5,000 stupid students to disregard law and order in Soweto. . . . We are going to bring the school situation back to normal."

The newspaper also quoted Coetzee as saying it was "quite possible" that as many as 50 pupils between the ages of 7 and 10 had been arrested.

Hundreds more students were picked up today, many of them at Fidelitas High School in the township known as Diepkloof. Witnesses said most of the students, along with three teachers, were arrested on school grounds, throwing the entire school into chaos. They were hauled off to Moroka station in four Army vehicles.

"They came and took us right out of class," said Viviens Davis, 16, who was held for about five hours today before his release. "They didn't tell us anything, they just made us move into trucks."

A police spokesman in Pretoria at first said that there had been only 600 arrests over the last two days, but later revised that figure upward to 881 -- 339 yesterday, 542 today -- with all but six later released. Parents and clergymen in Soweto had said the figure was at least 1,000, according to the Rev. Joe Seoka, a local Anglican priest.

"They've just been picking up children at random," said Leah Tutu, the bishop's wife and a Soweto resident, who was also at the scene today. "Some were even picked up in their own yards at home while they were playing with friends."

The police spokesman said students under 13 had been released without charge while others had been charged under the emergency regulations and released to their parents' custody. They are to appear in court early next week.

Before Tutu, Seoka and other clerics negotiated the release, tensions at the Moroka station appeared ready to boil over. Hundreds of parents, some saying they had been seeking access to their children for two days, stood outside the station, the entrance of which was guarded by two dozen helmeted white soldiers wielding R4 automatic rifles. At least a half dozen police dogs, mostly German shepherds, also guarded the grounds.

The soldiers periodically made forays into the street, driving back the crowd. At several times, a police bullhorn warned the parents in Zulu that police would use tear gas if they did not disperse. Journalists were also ordered to leave the scene or face arrest.

"The situation is very volatile and getting out of control," said Seoka at one point. "Rather than resolving the problem, the soldiers are actually working people up. They're provoking trouble."

The showdown never came. Instead, children eventually started trickling out of the station to wild cheers from the crowd. Tutu, the Nobel Peace laureate, said the local police commander at Moroka, Brigadier E.E. Oosthuizen, had been "very reasonable" in arranging the release of the students at his station before nightfall. Tutu said he would phone Oosthuizen tonight to thank him for his efforts.

Soweto, a series of townships outside Johannesburg in which more than 1.5 million blacks live, has been relatively quiet during this past year of nationwide unrest, reflecting both the area's greater affluence and divisions within the black community here about the most effective strategy to oppose white rule. But a recent series of incidents has prompted the police to announce a new curfew and the school restrictions evidently to head off trouble before it begins.

But residents contend the new measures -- and in particular the children's arrests -- have only exacerbated tensions here. "They are trying to instill fear in people, but in fact they are only making them more agitated," said Seoka.

"They're just inviting us to get into the whole thing," said a burly taxi driver who stopped at the sight of the soldiers to shout curses at them. He said his 7-year-old son had been afraid to attend school today because three classmates had been picked up yesterday.

"It hurts me," said the man, who would not divulge his name. "I grew up in Soweto and I never saw an Army. Today our children are seeing one on our streets."

In a tacit acknowledgement that the new regulations may have been too severe, Coetzee announced today he was shaving two hours off the nightly Soweto curfew so that late-shift workers can get to their homes and early shift workers can get to work unhampered. The new curfew applies from 11 p.m. until 3 a.m.

Police also announced they had arrested 94 more people using their broad emergency powers, bringing to 2,229 the number detained since the decree took effect July 21. They reported 1,183 of the detainees have been released