After 30 years of sectarian violence, this divided British province opened a new chapter in its troubled history today with the formation of a cross-community government with equal numbers of Protestants and Roman Catholics.

Backers of the Good Friday peace plan were firmly in control as Northern Ireland's legislature nominated a 12-member cabinet that includes a man said to be a former Irish Republican Army gunman and two veteran politicians who have been targeted by IRA assassination squads.

Whether such traditional enemies can work together remains to be seen. But after bitter decades in which more than 3,500 men, women and children were killed in political violence, there was a palpable feeling here that a new era of cooperation was at hand. Just five months ago, when the same legislature met for its first try at picking a cabinet, the session ended in failure amid a torrent of insults and catcalls. Today's meeting was, for the most part, quiet and businesslike.

The selection of the provincial executive, or cabinet, is one of a sequence of steps organized by the architect of the peace process, former Senate majority leader George Mitchell. Mitchell's careful choreography, with formation of the local government to be followed by steps toward IRA disarmament, was a central reason the legislature succeeded today.

The session was held behind the imposing Ionic columns of Stormont Castle, the provincial parliamentary hall. When Stormont was dedicated in 1934, the leader of the province, Lord Craigavon, declared proudly that the building would house "a Protestant parliament for a Protestant state." In sharp contrast, the assembly members who gathered at Stormont today represent "all the people of our province, in all their variety," said Seamus Mallon, a leading Catholic politician.

The cabinet named today, which will formally assume governing authority later this week, comprises six Protestants and six Catholics. All six Protestants are unionists--they want to continue Northern Ireland's political union with Britain. The Catholic members are from the republican and nationalist camps--they want to break with Britain and merge with the Republic of Ireland to the south. Two cabinet members are women.

The most striking evidence that Northern Ireland's long struggle has moved out of the street and into the cabinet room came when Sinn Fein, the political party affiliated with the IRA, named its first cabinet nominee: Martin McGuinness. The local media and histories of the IRA describe him as a former commander of an IRA guerrilla unit. McGuinness, who was named education minister, won't discuss these reports.

The nomination sparked a mild outburst of hissing from the unionist side of the assembly chamber, and three unionists stormed out in protest. Minutes later, though, the hardest of the hard-line unionist parties, the Democratic Unionists, nominated their own cabinet members: Nigel Dodds and Peter Robinson, both of whom were once unsuccessfully stalked by IRA gunmen. Dodds and Robinson indicated they will take part in cabinet meetings with McGuinness and other republicans.

The new legislature and cabinet were set up by the April 1998 Good Friday agreement, which creates the new power-sharing government and requires that paramilitary groups give up their weapons. Almost no disarmament has taken place.

The largest Protestant party, the Ulster Unionists, said they will withdraw from the new government if the IRA does not start disarming by February. Since the governmental institutions cannot function without the involvement of both the Protestant and Catholic communities, a withdrawal by the Ulster Unionists would shut down the government.

Still, the biggest divide was not between unionists and nationalists, but between the parties that favor the peace plan and the minority parties--all unionist--that oppose it.

The changes that have swept this province since Good Friday of 1998 were dramatically evident today in the diminished stature of the Rev. Ian Paisley, the forceful and outspoken leader of the self-described "No-Men," or opponents of the agreement.

For two decades, Paisley was the strongman of the unionist community, and thus the most powerful politician in Ulster. Today, he couldn't even get a motion to the floor of the assembly. When Paisley proposed to ban Sinn Fein from the cabinet, the presiding officer questioned whether he had the support necessary to introduce a motion.

To meet that test, Paisley would have needed 30 backers. But when he called on his supporters to stand, only 28 people in the 108-member assembly were willing to stand up with him.

The motion to bar Sinn Fein was a non-starter. And for the first time anyone here can remember, the bellicose Paisley was speechless. He sat quietly thereafter, watching the proceedings with a sheepish grin.

Over the next two days, the British government in London will give final approval to legislation transferring governing authority for Northern Ireland to the new legislature and cabinet. Meanwhile, the Irish Parliament in Dublin is to approve a bill that amends the Irish constitution, removing the clauses that assert a territorial claim over the six northern counties that comprise Northern Ireland.

On Thursday, the new government will formally take power. The same day, the IRA is expected to name a representative to the board overseeing disarmament, another historic development set up by the Good Friday agreement.

CAPTION: Sinn Fein's Martin McGuinness, allegedly a former IRA commander, addresses reporters after being named new education minister.