A hard-line Protestant member of the British Parliament from Northern Ireland was assassinated by Irish nationalist terrorists in Belfast today, hours after the London home of Britain's attorney general was bombed.

The Provisional Irish Republican Army claimed responsibility for both attacks at the end of one of the bloodiest weeks of its stepped-up campaign of violence aimed at ending British rule of Northern Ireland. Three people were killed and five injured in attacks on British and Ulster Protestant security forces in Northern Ireland earlier this week.

The Rev. Robert Bradford, 40, a Protestant Ulster Unionist member of Parliament from south Belfast, was shot seven times by several gunmen as he talked to elderly pensioners at his weekly meeting with constituents in a community center. The gunmen also shot and killed the center's youth worker as he rushed to Bradford's side.

The gunmen pushed past screaming children, who were attending a community center dance in the next room, and escaped in a waiting car as Bradford's police bodyguard drew his gun and fired at them, according to police and witnesses.

Fearing that the attack could touch off another wave of revenge killings, Ulster police and Britain's Northern Ireland secretary, James Prior, appealed tonight for calm. Speaking on television, Prior asked Protestants "to place your trust in the security forces and not let justifiable anger be vented on other equally innocent people."

By late tonight, five other persons had been injured in shootings in Belfast and Londonderry, including two policemen patrolling a Catholic area of West Belfast, United Press International reported. The policemen were not seriously hurt, but authorities said a 19-year old youth was critically wounded in another shooting in North Belfast.

In a statement by its Belfast brigade claiming responsibility for killing Bradford, the Provisional IRA accused him and the paramilitary Protestant Ulster Defense Association of being responsible for murders of Irish Catholics by Protestant terrorists in Belfast this summer and autumn. The IRA statement claimed Bradford was "one of the key people responsible for winding up the Protestant loyalist paramilitary machine in Northern Ireland . Let the UDA know well the cost of killing innocent nationalist people."

Bradford was best known for demanding summary executions of captured Irish nationalist terrorists. He was a member of Parliament for seven years and a Methodist minister who had split from the church.

Bradford was the second British legislator assassinated by Irish nationalist terrorists in three years. A Conservative member of Parliament, Airey Neave, was killed by a bomb by the Irish National Liberation Army in March 1979.

Prime Minister Margaret Thatcher said, "We shall pursue with the utmost vigor those who committed this wicked act and will persevere in our overriding duty to cleanse our country of the evil of terrorism."

The Provisional IRA claimed responsibility for last night's apparent attempt to kill another member of Parliament who is also the attorney general, Sir Michael Havers. Two bombs exploded against the back of his home in the fashionable south London suburb of Wimbledon, causing considerable damage. Havers and his family were away from home at the time, but a police officer guarding the house was injured.

It was the fourth IRA bomb attack in London in five weeks. Three people were killed and nearly 40 injured in bombings of a bus carrying British soldiers in the Irish Guards regiment, the car of a senior British general and several stores in central London's busiest shopping district.

The new terror campaign began after the abandonment of a seven-month hunger strike by convicted Irish nationalist terrorists in the Maze Prison outside Belfast.

The terrorist offensive also could be aimed at new efforts by the governments of Britain and the Republic of Ireland to improve relations and create conditions that could eventually persuade Ulster Protestants to agree to a new relationship among Ireland, Britain and Northern Ireland.

The Provisional IRA, like militant Ulster Protestant unionists, opposes such attempts at cooperation between Ireland and Britain. The IRA demands immediate British withdrawal and Irish unification, while militant unionists oppose any change in British rule except establishment of a Protestant-majority provincial government.

Prior pledged in a statement after the Bradford killing to do everything possible to end "the cancer of terrorism within Northern Ireland."