Moving to take advantage of what is seen as a brief "window of opportunity" for sectarian compromise in British-ruled Northern Ireland, the Thatcher government is launching another effort to give Ulster limited home rule with some share of power for the Catholic minority.

Britain's secretary for Northern Ireland, James Prior, said today he believes moderate Protestants and Catholics have been given a new, if possibly fleeting incentive to narrow their political differences by the recently increased influence of extremists on both sides.

The deaths of hunger strikers in the Maze Prison in Belfast earlier this year increased sympathy among the Catholic Irish-nationalist minority for Provisional Irish Republican Army militants while the IRA's subsequent step-up of terrorism caused a backlash among the Protestant unionist majority, aiding hard-liners.

Explaining his previously unannounced initiative to American reporters, Prior said the next "month or two" of intensive, informal negotiations with Ulster leaders "will help us decide whether we will be able to make some progress."

British government officials said Prior is not seeking complete agreement on a new home-rule plan, which has proved virtually impossible to achieve in the past. The Protestants have insisted on unfettered majority rule while the Catholics have demanded a guarantee of a sizable share of executive power they could never achieve at the polls as a perpetual one-third minority.

Instead, the officials said, Prior is trying to convince the two sides to narrow their difference and "agree to disagree" about the remaining gap.

Prior said the government had ruled out any further integration of Ulster into Britain, "because it is not another Yorkshire or Norfolk."

But he emphasized that both Dublin and London had agreed that Ulster could never be integrated constitutionally with Ireland without the consent of a majority there.