Bobby Sands, a jailed militant of the Provisional Irish Republican Army, died early this morning in the 66th day of a hunger strike in support of demands that hundreds of convicted IRA terrorists in British-ruled Northern Ireland be treated as political rather than criminal prisoners.

His death immediately touched off widespread rioting in the Catholic ghettos of West Belfast. As whistles sounded by apparent prearrangement, hundreds of mostly young people filled the streets, attacking the armored vehicles of police and British Army patrols with stones and Molotov cocktails in the early morning darkness.

A number of buildings, including factories, a bank and a church, were set afire. Firemen responding from around the city also were stoned and prevented from fighting some of the blazes. Police wearing bulletproof garments fired plastic bullets into the crowds to try to disperse them and protect the firemen.

Sands, 27, who had been elected a member of Parliament in Ulster during his hunger strike, died at 1:17 a.m. in the Maze Prison 10 miles southwest of Belfast. Supporters said he was clutching a golden crucifix given him by the pope's personal envoy, the Rev. John Magee, who visited Sands three times last week but failed to persuade him to give up his hunger strike.

"He took his life by refusing food and medical intervention," a British government statement said.

His weight had dropped from 155 pounds to 95 pounds in the last two months on a diet of salt and water.

It is believed that his mother, Rosaleen, and sister, Marcella, were in the prison at his bedside. His mother had told reporters last week that she would obey her son's wishes and refuse treatment or intravenous feeding to the end.

Sands had been in a coma since Sunday, when his mother publicly appealed for the people of Northern Ireland to remain calm after his death. Government officials and Catholic and Protestant politicians and community leaders also have urged people to avoid a surge of the sectarian violence Ulster has suffered for 12 years.

Tight security precautions have been in effect here and in parts of the rest of Britain for several weeks. In Belfast, where fears of violence have been highest in the interspersed Catholic and Protestant ghettos, police and British Army patrols have been out in force. Many streets have been closed or posted with roadblocks to contain any rioting or attempted attacks by one community or another.

Until news of Sands' death spread through the Catholic ghettos at the end of a long May Day holiday weekend, the streets of western Belfast, where the worst trouble was expected, were unusually empty as police officials appealed to parents to keep their children home. They also tried to discourage television crews and photographers from converging on areas where youths had congregated because, one police commander said, their presence encouraged the attacks on passing vehicles and patrols.

Prime Minister Charles Haughey of the neighboring Republic of Ireland made what he called an "11th hour" appeal yesterday to the European Commission on Human Rights to recommend some from of compromise between Sands' demand for greater freedom for terrorist prisoners and the British government's refusal to give any ground toward political prisoner status. The commission reportedly was ready to meet later today, but Sands' family repeated through a spokesman its refusal of such intervention at Sands' previous insistence.

Pope John Paul II's envoy also had failed last week to persuade Sands to give up his hunger strike. In his Sunday address to crowds in Rome, the pope said, "I ask you to pray for our Catholic and non-Catholic brothers in Northern Ireland, who are living through hours of growing tension, which it is feared might explode in new and very serious acts of fratricidal violence."

Britain's Northern Ireland Secretary, Humphrey Atkins, said in a statement shortly after the announcement that Sands had died, "I regret Sands' death. Too many have died in Northern Ireland. His death was self-inflicted."

Sands had spent a third of his life in prison, after joining the provisional IRA as an unemployed teen-ager. He was born in a Protestant area of Belfast, but when sectarian violence began in 1969, his family has said, they were forced out and moved to public housing in a Catholic area known as IRA recruiting ground.

Sands was first arrested in 1972 and convicted of involvement in a series of robberies for the IRA. He served less than four years in "special category" status in what resembled a prisoner of war camp then used by the British government for both Catholic Irish and Protestant Ulster militants convicted of terrorism.

After less than a year back on the streets, Sands was convicted of gun possession following his arrest near the scene of an IRA bombing and gun battle with police. By this time, special category status had been abolished for all newly convicted terrorists, and Sands was imprisoned in one of the H-shaped, high-security cellblocks of the Maze.

It is one of the most modern prisons in Europe, but Sands and other convicted terrorists have resented its denial of the freedom of dress and movement still enjoyed by old special category prisoners in the nearby camps of Long Kesh. Sands joined hundreds of convicted terrorists prisoners in escalating protests during the past four years to demand rule changes regarded by the British as giving terrorist political prisoner status.

After being chosen by the IRA as a spokesman and leader of the protesting prisoners, Sands began his hunger strike March 1. He was later joined by three other Irish nationalists. Francis Hughes, 27, a convicted murderer, has been on hunger strike for 51 days and is now reportedly very weak. Raymond McCreesh, convicted of attempted murder, and Patrick O'Hara, convicted of possession of a hand grenade, both 24, stopped eating 45 days ago.

On April 9, while he was on his hunger strike, Sands was elected to a vacant seat in the British Parliament from an Ulster constituency with a small Catholic majority on the Irish border.It was a well-engineered propaganda coup by the IRA, which outmaneuvered or forced other Catholic candidates out of the race against a staunch Protestant unionist.

Since then, legislation has been introduced to disqualify convicts serving prison sentence for eligibility for Parliament. If quickly passed, it would prevent another IRA hunger striker from being put up as a candidate now that Sands' death has again left the seat vacant.

His election and fears of violence after his death drew international media attention to Sands' hunger strike. This has been resented by both moderate Catholic politicians who advocate peaceful unification of Ulster with Ireland and by Ulster Protestants who point to the IRA's continuing assassination campaign against them.

Thirteen people died in sectarian violence in Northern Ireland during Sands' hunger strike:

They are six police officers and Protestant reservists in the Ulster security forces assassinated in separate incidents by terrorists; a 40-year-old man apparently mistaken for a Protestant reservist; a 29-year-old woman census taker believed murdered by an IRA gunman, although the IRA denies it; a 26-year-old Catholic man believed murdered by Protestant terrorists; a 20-year-old Catholic man driving a stolen car who was shot by a pursuing security patrol; two Catholic teen-agers killed by a speeding British Army landrover during riots in Londonderry, Northern Ireland's second-largest city, toward the end of Sands' hunger strike; and a 15-year-old Catholic boy hit by one of the plastic bullets fired by police during the riots.

[In a statement released in Washington soon after Sands' death was announced, the State Department said it "deeply regretted" Sands' death and hoped the other three hunger strikes would not end in the same "tragic fashion."]