A nail bomb hidden in a parked laundry truck exploded outside a British Army base in central London today, killing an elderly woman passer-by and injuring 40 soldiers and neighborhood residents, two of them children.

The Provisional Irish Republican Army, bitter foe of British policy in Northern Ireland, immediately claimed responsibility for the act.

Today's death was the first in an Irish terrorist bombing here since a senior Conservative Party member of Parliament, Airey Neave, was killed in March 1979 in the House of Commons garage.

Scotland Yard's antiterrorist chief warned that today's bombing could be the start of a new campaign of terrorism in England following the end of a seven-month hunger-strike campaign by Provisional IRA prisoners in British-ruled Northern Ireland. There were several bombings of government offices and businesses in Ulster yesterday.

The nail bomb was detonated, apparently by remote control, shortly after noon as an Army bus was passing by carrying 23 Irish Guards. The guards, in their red dress uniforms, were returning to Chelsea barracks from ceremonial duty at the Tower of London.

All but one of the soldiers and a score of other people on the street and in surrounding shops, public housing and a pub were hit by flying six-inch nails, bolts, glass and other debris from the blast. Eight of the soldiers were reported to be seriously injured, one critically. A hospital spokesman said the injuries "were some of the worst we have seen here."

"We went past this truck and everything just went up in smoke," Cpl. Brian McAllister said after being treated for arm and face injuries. He said the soldiers on the bus were hit by nails and glass in the "face, chest, back, arms, everywhere."

Four hours after the blast, in a statement issued by the Irish Republican News Bureau in Dublin, Ireland, the Provisional IRA claimed responsibility for the bombing. Its last in mainland Britain was in January, when a Provisional IRA bomb wrecked a barracks at a Royal Air Force base on the edge of London, injuring two.

The Provisional IRA largely abandoned random, heavy-casualty bombings of public places such as stores and pubs in England after 1976. Most of its acts of terrorism in mainland Britain since have been assassination attempts and attacks on military targets.

The Provisional IRA statement said today's attack was "aimed at a party of British soldiers," the busload of Irish Guards. Because the Irish Guards regiment is composed mostly of Irish volunteers, it has never been among the British troops serving in Ulster.

The Chelsea barracks, a walled city block of modern, red-brick-and-glass administration and apartment buildings, is in a busy neighborhood near the Thames River, not far from Victoria train station, fashionable Eaton and Sloane squares, and the Kings Road shopping district.

The streets and shops were full of people when two men were seen pushing what appeared to be a disabled laundry truck to the curb across the street from the southeastern corner of the Chelsea barracks. A neighborhood resident helped push .

About 40 minutes later, the bomb exploded as the military bus passed. Both vehicles were wrecked, and glass from the windows broken nearby badly cut a 5-year-old boy and a 2-year-old girl, among others.

Nora Field, 61, a widow who lived in nearby public housing, was killed while talking to another neighborhood resident, Hazel Cole, who escaped injury. "The explosion was behind me," said Cole, 27, who is six months pregnant. "The other woman took the full force of it."

Sandra Aranha saw the "extremely loud" explosion from a travel agency office. "I ran out," she said, "and there were people lying everywhere and children were screaming." She said her employer, Michael Russell, was injured when he "ended up with a lot of our front window in him."

The Provisional IRA statement said, "The attack is attributable to the state of war which exists between the British government who occupy Northern Ireland and the oppressed Irish people who strike out through the Irish Republican Army. We await the hypocrisy which will undoubtedly follow from British political leaders whose attitude to Irish victims of their violence in our country only strengthens our conviction in our cause and methods."

There had been speculation in Northern Ireland that the Provisional IRA would step up its paramilitary campaign and strike in England to demonstrate that it had not been defeated by the failure of the hunger strikers in the Maze Prison to win prisoner-of-war treatment.

Further concern was created in Ulster by what police believed to be an attempt by Protestant terrorists to kill Irish Catholics in a Belfast drinking club Thursday night. Two hooded men fired indiscriminately with a machine gun and pistol into several hundred people in the Shamrock social club. They killed four persons, one of them a City Council member, before being driven out of the club by a barrage of beer bottles and glasses.

The club is in a small Irish Catholic neighborhood called The Ardoyne, which is isolated in an otherwise-Protestant, working-class area of Belfast. Ardoyne residents feared throughout the hunger strike that they would be attacked by Protestants. Thursday night's shooting follows the random killings of two other Irish Catholics in The Ardoyne in recent months.

Both Catholic Irish-nationalist and Protestant British-loyalist members of the Belfast City Council condemned the pub attack. Provisional Sinn Fein, the political arm of the Provisional IRA, called it an act of "political terror."