Prime Minister Margaret Thatcher extended an olive branch today to leaders of Northern Ireland's largely Protestant unionist community, hoping to defuse growing tension and plans for a protest strike in the province Monday.

Unionist leaders James Molyneaux and Ian Paisley promised only to "reflect" on her offer to set up new mechanisms to consult with them more closely on Northern Ireland affairs. But following the 90-minute meeting with Thatcher, they appeared to draw back from the brink of outright confrontation with the British government over November's Anglo-Irish accord giving the Republic of Ireland to the south a voice in the province's affairs on behalf of its minority Catholic community.

For its part, the government responded favorably to a unionist proposal to hold a roundtable conference among the main Northern Ireland parties to discuss increased "devolution," or home rule, in the province. They agreed to meet again shortly.

Roman Catholic and centrist leaders and the Dublin government welcomed the developments.

Northern Ireland Secretary Tom King hailed today's talks as "suddenly, a chance to look afresh at a range of opportunities."

Both Thatcher and the unionists insisted that any new arrangement between them would not affect their diametrically opposed positions on the peace-keeping agreement signed last November between London and Dublin. The agreement set up an intergovernmental body between the two for regular meetings on the adminstration of Northern Ireland.

Leaders of the unionists -- so called because they favor continued union with Britain -- have rejected the accord outright on grounds that it violates British sovereignty. By giving a foreign power a voice in their government, they contend, it makes them second-class citizens in the United Kingdom. Ultimately, they fear, it could lead to reunification of the island under Irish sovereignty.

A joint statement following today's meeting said that Thatcher "reaffirmed the government's commitment to the implementation of the Anglo-Irish agreement." But in a news conference after the talks, Molyneaux and Paisley insisted that the proposals under consideration were completely separate from the three-month-old agreement.

"We don't want anybody to think we accept it," Molyneaux said. But, he acknowledged, as a result of today's talks, "we have got away . . . from a deadlock situation."

Under today's proposals, Thatcher offered unspecified "arrangements" under which unionists would be consulted before and after regular talks with Dublin under the agreement -- in effect, the current arrangement between Dublin and the Northern Irish Catholics.

She also offered "consultations" on parliamentary changes that would help boost Northern Ireland to the status of Wales and Scotland in law-making procedures here, and on a future role for the moribund Northern Ireland Assembly as a local government mechanism.

The proposed roundtable talks on devolution would include the two main unionist parties, the mainly Catholic Social Democratic and Labor Party and two smaller centrist groups. But it is believed they would exclude Sinn Fein, the political arm of the outlawed Irish Republican Army.

The last attempt at home rule in the province failed in 1974, when a Protestant protest strike brought Northern Ireland to a standstill.

Today's talks were the first between Thatcher and the unionist leaders since the 15 unionist members of the British Parliament resigned their seats to protest the agreement and forced last month's by-elections in the province.

Both sides described the meeting as "tough." But the emergence of the apparent beginnings of an accord was an indication of a shared belief that the situation in Northern Ireland may be getting out of hand.

Molyneaux, of the Ulster Unionist Party, and Paisley, of the Democratic Unionists, have been in the forefront of urging Protestant rejection of the accord.

So far, however, they have achieved little. Turnout in the by-election -- which they had billed as a referendum on the agreement -- was less than expected, and one unionist seat was lost to a Social Democratic candidate.

Other militant Protestant groups, however, including the traditional Orange Order and the newly formed Ulster Clubs have advocated a more militant campaign of rejection. Protestant paramilitary organizations have been actively recruiting and advocating more direct action.