London — Only a month ago, the affairs of Northern Ireland seemed to be moving into a more tranquil phase. Today the men of violence and extremism have suddenly regained the initiative. Some British officials now say the situation in Ulster is probably as bad as it has ever been since the current round of sectarian strife started 12 years ago.
In Northern Ireland itself there is a renewed wave of murders - and retaliations. Once again the bombings have reached across the Irish Sea to London.
In Whitehall, British civil servants worry that the latest efforts to find a political way out of Northern Ireland's strife have been gunned down in the extremist cross-fire.
In the House of Commons, amid recrimination and uproar, three Protestant Ulster Unionist members have been suspended for disorderly conduct, among them the Rev. Ian Paisley, leader of the Ulster Unionist Party.
Enraged by an escalating terror campaign by the Provisional wing of the illegal Irish Republican Army (IRA) and by closer political contacts between London and Dublin, Paisley and his followers have said they will set out to make it impossible for Prime Minister Margaret Thatcher's government to run the province.
The appeals for calm issued by Mrs. Thatcher and her Northern Ireland secretary, James Prior, so far have fallen on deaf ears. Pointing to the horrors in store should a wider civil war between the Roman Catholic and Protestant communities become a reality, the British leaders took swift action on two fronts:
1. A comprehensive review of security arrangements following the murder by IRA gunmen of an Ulster member of Parliament and a bomb blast at the London home of the British attorney general.
2. An urgent reassessment of political attitudes toward Northern Ireland.
Twenty thousand police in London and the surrounding counties were ordered immediately to check tens of thousands of lockup garages in a search for 500 pounds of explosives believed to be secretly stockpiled by the IRA. Guards protecting Cabinet ministers and leading politicians were stepped up in case of new attacks.
But it was the political review that Mrs. Thatcher regarded as the highest priority.
Mr. Paisley's vow to render Northern Ireland ungovernable by transferring his political campaign from the British Parliament in Westminster to Ulster itself is considered here to be no idle threat. It was accompanied by talk of building up a ''third force'' of Protestant paramilitary activists dedicated to hunting down IRA gunmen and bombers and dealing with them.
On at least one previous occasion, Mr. Paisley has brought public life in Ulster to a standstill by calling for strikes and demonstrations. Here in London the government has already begun adjusting to the possibility that Paisley could again lead an effective campaign of noncooperation.
Paisley, meanwhile, called a meeting of Unionist supporters in Belfast and urged counselors and other local officials to shun all contacts with Mr. Prior and his officials. He also arranged for recruits to his ''third force'' to mount token displays of strength in a number of areas.
These moves created genuine alarm in London where Mrs. Thatcher and her ministers find themselves squeezed between millstones.
On the one hand, the new crisis has arisen as a result of a determined IRA campaign to whip up violence both in Ulster and in Britain. Mrs. Thatcher at first thought she could cope with the new campaign from that quarter by upgrading antiterrorist measures, including the possibility of deploying more crack Special Air Service troops in Ulster itself.
On the other hand, she came under pressure almost immediately from the opposite direction. Her talks in London two weeks ago with Irish Prime Minister Garret FitzGerald aroused Protestant fears of a secret deal with Dublin, possibly leading to the unification of Ireland.
At the same time, outraged by the IRA violence campaign, Protestants struck back with revenge attacks of their own. Despite Mr. Prior's pleas for calm, the murder of the Rev. Bradford sparked off a number of revenge attacks, presumably by Protestant extremists, including two killings. (Reuters reports that Mr. Prior was jostled and abused, but not hurt, by a hostile crowd of Protestant mourners when he arrived unannounced at Mr. Bradford's Belfast funeral Nov. 17.)
One commentator pinpointed Prime Minister Thatcher's dilemma by noting that tougher measures against the IRA would probably alienate the Catholic minority in Ulster, but that a failure to act toughly could rouse the entire Protestant majority to rebellion.
This has led many people caught up in the Ulster crisis to conclude that appeals for calm, unless accompanied by new political initiatives, are not enough.
And yet, reviewing the political options, Mrs. Thatcher cannot be happy at the choices open to her.
One option would be to ask Prime Minister FitzGerald, south of the border in the Irish Republic, to take more vigorous action against IRA supporters who are helping the IRA's gunmen in the north to escalate the violence. But the Irish prime minister has already told her that it would be politically difficult for him to do more than he is doing now.
Another option would be to urge the administration of President Reagan to curb the activities of IRA sympathizers in the United States, so that money available to the men of violence would flow less freely. Mrs. Thatcher, however, has already discreetly asked for Reagan's help, seemingly with little immediate effect.
A third option might be to try to prevail on Mr. Paisley and other Unionists to draw back from their apparent commitment to making things as difficult as possible for the British government. But the Protestant leader has never been in an angrier mood. His remarks after expulsion from the House of Commons were violent in the extreme, with talk of Thatcher ministers being ''traitors.''
Speaking on the day Paisley stormed out, Mrs. Thatcher declared ''revenge is no policy. Hatred gives birth only to hatred. Reconciliation is the path to peace.''
Unhappily for the prime minister, revenge and hatred are now occupying the center ground of Ulster politics and reconciliation has been thrust into the shadows.