Political uncertainty in Northern Ireland fuels increase in terrorist violence

While James Prior, secretary of state for Northern Ireland, has been visiting the United States, trying to tell Americans the good news about Ulster, he has had to contend with a rising tide of violence and mayhem here at home.

Dark winter nights have always brought an increase in the death rate from terrorism. But this time there are fears that political instability is adding to the perennial problem.

Mr. Prior took a calculated risk when he launched his plan for a new 78 -member Ulster assembly, elected Oct. 20. All the signs so far are that he miscalculated.

He wanted to get the warring Unionist (favoring continued union with Britain) and Nationalist (favoring reunification of Ireland) politicians together and give them a chance to agree on a transfer of power from London to Belfast on a power-sharing basis. Instead, they have moved further apart.

None of the 19 Nationalists elected - 14 Social Democratic and Labour Party (SDLP) moderates and five Sinn Fein extremists - attended the opening of the new assembly Nov. 11. They are pledged to continue their boycott indefinitely in the hope of bringing the assembly down.

Meanwhile, the Unionists are proceeding to set up assembly committees without them, ignoring the fact that nearly 30 percent of the electorate is being left unrepresented.

One of the most significant features of the Oct. 20 election was the 10 percent vote for Sinn Fein - the political arm of the the Provisional wing of the illegal Irish Republican Army - and the boost this has given to the republican terrorists.

Because of the way the party fought its campaign - ''with a ballot paper in one hand and an Armalite [rifle] in the other'' - there is no disputing that the IRA now has considerably more support in the Roman Catholic community than was suspected. The effect can be seen in the statistics. Since Oct. 1, the death toll this year has jumped from 50 to 72, including 15 since the election results were announced Oct. 22. Between them, the IRA and another republican faction, the Irish National Liberation Army, have killed six policemen in three weeks.

Even the news from America has helped raise community tensions, by encouraging republicans and angering Unionists. The acquittal of five men in New York, who admitted stockpiling guns for the IRA, was given wide coverage in the media. The connection between the ostensibly charitable US organization, Noraid, and guns was proved; but there is widespread frustration among non-republicans here that the American court system could not get a conviction.

Protestant paramilitary organizations have hit back with random killings of Roman Catholics, but their methods have been counterproductive.

Tit for tat assassinations have plagued Ulster for years. But the seriousness of the new wave is that it takes place against a background of political unrest. Nationalists are united in their desire to destroy the assembly at Stormont, while Unionists are determined to use it as a vehicle to attack the British government on security and to regain majority rule.

The embattled Mr. Prior has promised to let assembly members quiz him about government policies. He can only hope that the SDLP drop their boycott rather than risk further losses to Sinn Fein which has signalled its intention to fight the next election for seats in Parliament at Westminster. For the SDLP to back down, however, the party would have to win some concession from the British on closer links between Ulster and the Irish Republic - which would, in turn, alarm the Unionists.

The only possibility of a way out of the impasse seems to be the election this week of a government in the Irish Republic which is sympathetic to the low-key British approach. It is little wonder, therefore, that the British are praying for a win by Garret FitzGerald. His proposed solution is a Federal United Ireland, with consent of Northern Ireland's Protestants. The election of Charles Haughey, a staunch republican, would more likely continue the cold war between Dublin and London, and doom the Ulster assembly.