London — Prime Minister Margaret Thatcher must have felt a sense of deja vu when she was told of a car bomb exploding in Dulwich, south London. The device in the attack Oct. 17, which has gravely injured Lt. Gen. Sir Steuart Pringle, commandant of the Royal Marines, was not unlike the one that had killed her friend and colleague Airey Neave at the House of Commons in March 1979 not long before she formed her government.
It was the second London bombing by the Provisional wing of the illegal Irish Republican Army (IRA) on successive Saturdays. The first injured many of the soldiers at whom it was aimed, and killed two civilians as well.
Sir Steuart is the most senior British military victim of IRA terrorism since the troubles began in 1969.
It has been known for several months that the end of the H-block campaign would herald a new assassination campaign in Britain. London's first bomb went off just a week after the hunger strike ended on Oct. 3.
Taking responsibility, the IRA attributed it in familiar language to ''the state of war which exists between the British government who occupy Ireland and the oppressed Irish people who strike out through the IRA.''
British police had increased their bomb alert when the hunger strike ended, but they did not have specific warning and knew of no IRA unit in London. Now it's thought that from four to six IRA operatives, lying low since last winter's bombings here, have been assimilated into the community. The H-block campaign, which gained enormous public sympathy among Northern Ireland's Roman Catholics and in the United States, rejuvenated and unified the republican movement in the six provinces.
The new bombing campaign, on the other hand, has had the opposite effect: the Irish republican movement is more deeply divided than ever before.
The official Sinn Fein, political wing of the old, official IRA, has been trying hard to head off any renewal of violence. It has denounced the Provisional wing of the illegal IRA as ''fascists'' devoted to mindless violence.
Part of the far left in British politics, whose views are important in understanding the IRA and their international connections, has echoed this view.
Like the official Sinn Fein, the British left believes the terror campaign will be completely counterproductive and says that Ireland can be reunified only with the mass support of the people of both Ireland and Britain.
But even though IRA policy is dividing the republican movement, the IRA sees itself the movement's sole voice.
There is no clear way ahead, but one idea being talked about behind the scenes is to redraw the border to bring more Catholics south of it.