SYDNEY -- Kingsley Richard Dixon, a slight, 19-year-old aborigine, was found dead last July, hanging by a sheet from the bars of his cell window in a South Australian jail.

Six months later, despite a coroner's report that Dixon had committed suicide, his mother, Alice, says she remains convinced that he was murdered.

For the past two weeks she has sat in a crowded court in Adelaide, the South Australia state capital, and listened to the first of about 100 witnesses called by the government.

The Dixon case is the first brought before a government-appointed commission of inquiry to investigate how 98 aborigines have died in jail or in police custody since 1980. In almost all cases the coroner's findings have been suicide or "death by misadventure."

But relatives of several of the dead prisoners and representatives of the Committee to Defend Black People's Rights plan to testify that the deaths in custody were caused by abuse from police, jail wardens and fellow prisoners.

Since August, when retired Supreme Court justice James Muirhead was appointed to investigate the deaths, the number of alleged suicides has more than doubled and so, too, has the anger of aborigines.

Police have denied allegations of murder, and government officials, while deploring the situation, have said they would prefer to let the commission issue its report before commenting publicly.

Most of Australia's 300,000 aborigines live in rural areas, where the rate of unemployment ranges from 70 to 80 percent. But there are also urban aborigine communities in each of the six state capitals.

The continent has been the home of the aboriginal people for at least 40,000 years, while Australia last month celebrated the 200th anniversary of white settlement.

For years the aborigines have campaigned for greater influence in government decisions and for better treatment in general. While Australia's white population of 16 million has become much more sensitive to those demands in recent years, sweeping federal land-rights legislation, which would have granted ancestral land to tribal groups, was shelved in 1986.

In the current hearings, aboriginal leaders have complained of not having been consulted when the commission was established, and some groups have reiterated their threat to boycott proceedings unless the safety of witnesses is guaranteed.

Some of the more outspoken aboriginal leaders say they remain unconvinced by Muirhead's promise to provide key witnesses with full protection from retribution during and after their testimony.

According to a report by the Australian Institute of Criminology aborigines are 23 times more likely to be imprisoned than whites and are regularly jailed for trivial offenses, usually drunkeness.

Although making up only 1.3 percent of Australia's population, aborigines account for 15 percent of its prison population.

In Western Australia, where 29 of the 98 deaths have occurred, aborigines account for one-third of the state's prison population. "The aboriginal deaths as well as the numbers of aboriginals in our prisons are of a ratio which is unacceptable in a country . . . which professes an abhorrence for racial discrimination," Muirhead said.

Before the start of the hearings, Muirhead warned that unless the commission's membership is expanded, he will be unable to meet his deadline of next December. He also said that he feared more deaths of aborigines in custody before he can complete his task.

During the next 11 months, Muirhead will visit aboriginal communites in more than 30 towns and cities to investigate the circumstances of each reported death. He also will probe the subsequent activities of police investigators and coroners.

Eddie McGrath, who joined demonstrators outside Sydney's jail, said he feared that a cousin of his, under detention in the outback town of Griffith, could soon become a victim of police harassment.

McGrath, talking to reporters outside the jail, said that after his cousin was jailed, a warden took his shoes and socks. Moments later, McGrath quoted his cousin as saying, "a white cop walked in and said: 'Here are your socks. You want to hang yourself?' "