IN estimated 21 percent of inmates in state prisons in 1991 were serving time for drug offenses, compared with 9 percent in 1986, according to a Department of Justice survey released yesterday.
The survey of the state prison population, which increased 58 percent between 1986 and 1991, came from interviews with almost 14,000 prisoners in 45 states. Other findings:
* 16 percent of inmates were armed with a gun when they committed the offense for which they were imprisoned.
* 47 percent of prisoners were serving time for violent offenses, compared with 55 percent in 1986.
* 94 percent of inmates had been convicted of a violent crime in the past or had received a previous sentence of probation or incarceration.
* In 1991, 65 percent of inmates were from minority groups, up from 60 percent in 1986.
* Of all state inmates in 1991, 5 percent were women, up from 4 percent in 1986.
* More than half of all prisoners did not grow up with both parents. About one-fourth had parents who abused drugs or alcohol. Just under one-third had a brother who had served time in jail or prison.