Inmate death rates for suicide, homicide and AIDS are showing substantial declines in jails and state prisons, the government says. The trend reflects improved medical care and closer attention to separating violent criminals from other offenders.

State prison homicide rates declined by more than 90 percent, from 54 per 100,000 in 1980 to four per 100,000 in 2002, the latest year for which data is available, the Bureau of Justice Statistics said in a report yesterday.

Jail suicide rates fell more than 60 percent, dropping from 129 per 100,000 inmates in 1983 -- when suicide was the leading cause of death among inmates -- to 47 per 100,000 in 2002.

Death rates from AIDS-related causes in jails also fell sharply, from 20 per 100,000 in 1988 to eight per 100,000 in 2002. In state prisons, AIDS-related death rates fell from 100 per 100,000 inmates in 1995 to 15 per 100,000 in 2000.

One reason for the downward trend is that advocacy groups have become much more aggressive in filing lawsuits to improve conditions behind bars, said Kara Gotsch, public policy coordinator for the American Civil Liberties Union's National Prison Project.

The prevalence of gangs in prisons has resulted in a lot of violence, prompting corrections officials to pay more attention to classifying prisoners, Gotsch said.

"There's much more awareness about the problem of suicides in jails," said Lindsay Hayes, project director for the National Center on Institutions and Alternatives. "Twenty years ago if you asked a sheriff, he wouldn't have any information on it or any sensitivity to it. It wouldn't be on his radar screen."

Today, screening and training have improved, and the mental and medical health staffs are better, Hayes said.

The improvements are occurring as the size of the population behind bars heads upward.

The number of inmates has been increasing since the 1980s, with the prison and jail population now at 2.1 million.