Scores of officers shielded by clouds of bullets and tear gas swept through two prisons yesterday to end uprisings by youthful offenders in Michigan and high-risk criminals in Nevada.

Meanwhile, inmates of the world's largest walled prison, the Southern Michigan Prison in Jackson, were back in cells after a day of rioting that officials called the worst in almost three decades.

Three guards taken hostage at the Maximum Security Prison near Carson City, Nev., were released unharmed, while 42 inmates and four prison guards were hurt before Michigan authorities regained control of the prison and the state reformatory 75 miles away in Ionia. The disturbances broke out when inmates thought they were going to miss holiday meals and recreation time because of a "lockdown," officials say.

Nevada authorities launched an investigation to determine how the inmate accused of taking the hostages at Carson City got a gun into his cell block.

The uprising, which involved 23 inmates, some on Death Row, ended before dawn when guards spraying bullets from automatic weapons pushed the prisoners back into their cells. The guards were freed after 10 hours when prison officials agreed to give inmate David (Bang Bang) Wayne a sedative and let him talk to his girlfriend.

In Ionia, Dale Foltz, warden of the Michigan Reformatory, said his youthful charges would be responsible for cleaning up the mess left by their eight-hour rampage. That melee ended yesterday when guards and state troopers, firing tear gas, herded the inmates back into their cells.