Four student leaders, convicted last week of sedition for their participation in the unrest that gripped the teeming all-black township of Soweto in 1976 and 1977, were today given jail sentences of up to four years.

Seven other defendants, also former high school leaders in the black residential area outside Johannesburg, were given suspended five-year sentences at the close of one of the most closely watched political trials in South Africa in recent times.

The trial of the "Soweto 11," in effect, was the government's attempt to establish that "agitators" were to blame for the violent protests in black communities against the use of the Afrikaans language in school, against the black's inferior school system, and finally against the government's racially discriminatory policy of apartheid.

More than 700 people died in the unrest that lasted 16 months.

Black leaders contest this version of the causes of the unrest, saying it was a spontaneous manifestation of black anger at the inferior position they are assigned in the apartheid system.

The general reaction from many of the young blacks who travelled more than 35 miles to the court in an all-white suburb today, was that the 11 students should not be held responsible for the unrest.

The international attention drawn by the trial may be one of the reasons for the relatively light sentences by South African standards. In other parts of the country, judges are giving out sentences of eight to 10 years for politically motivated offenses such as encouraging young blacks to flee the country and join guerrilla group.

The defendants, 10 men and one woman, who range in age from 18 to 23, entered the courtroom today with raised clenched fists in the black power sign and sang a Zulu freedom song, "Azania, My Beloved Country." Azania is the blacks' name for South Africa.

Provincial Supreme Court Judge Hendrik Van Dyk said he took into account the age and time already spent in detention, running from 21 to 28 months, in suspending the sentences of seven of the students.

The longest sentence of four years went to Daniel Sechaba Montsitsi, 23, who was the fourth chairman of the Soweto Students' Representative Council, formed during the unrest to air student grievances. The council was later banned by the government. All its previous chairmen left the country to escape detention.

Van Dyk noted that Montsitsi, a person of "exceptional Talent, more than anyone else could have made Soweto a peaceful place in 1976 and 1977." Montsitsi has already served 23 months in detention, 13 of that in solitary confinement, but none of that time will be credited to his four-year jail sentence.

Van Dyk convicted the 11 students April 30 after giving one of the broadest definitions of sedition ever rendered in South African legal history. Van Dyk said sedition need not involve violence but can be merely the intention to subvert or defy the authorities, including the police and the education department.

Others who received jail sentences were Susan Sibongile Mthembu, 23, two years; Matison Morobe, 22, three years; and Seth Sandile Mazibuko, 19, two years. The defense said it would appeal the sentences.

In another development today, the editor of the black newspaper, The Nation, announced that the government has banned all future editions of the paper. The Nation is run by the political party of Zulu chief Gatsha Buthelezi, and widely read among the country's 5 million Zulus.