Just a year ago, Roy Mason, the cocky miner who runs Ulster for the Labor government, boasted:

"There can be no doubt that the tide has turned against the terrorists."

The Northern Ireland minister looked back with satisfaction on his year: bombings down, killings down, injuries down, security shifting from soldiers to police.

On this Christmas Eve, Mason is conspicuously silent. The Provisional Wing of the Iris Republican Army has launched a well advertised and nonlethal bomb spectacular in London and five provinical cities. This, moreover, seemed to climax a largely ignored campaign in Ulster itself where more than two bombs a day have been going off for the past two months.

But today, all Britain grimly focused on Ulster again. There the IRA staged its deadliest coup in two years, killing three soldiers on foot patrol in Crossmaglen, the center of a wild region was cut down by machine-gun fire from a panel truck, which raced away to safety.

It is now painfully evident that the Provisionals never died, are back in business and once again demonstrating their capacity to make headlines, if not win political concessions from Britain.

By past standards, the Rpovisionals are minumizing the human outrages that have cost them support among Ulster's Catholics and maximizing public values. To date, killings have been confined almost exclusively to Ulster soldiers, police and prison warders.

The bombs that began going off in England early Sunday are small, 10 pounds of gelignite or less. They were placed in shopping centers and timed to explode when these places are usually deserted. One, in Bristol, slightly injured seven late night revelers.But those in Southampton, Liverpool, manchester, Coventry and London have damaged property rather than persons.

A year ago, Mason was warned by veteran Ulster observers that his optimism was either naive or duplicitous. As long as the half million Catholics in the province continue to live as second-class citizens, systematically excluded from the better paying jobs in a dying industrial region, young men will continue to join the IRA.

Mason, a miner from Barnsley, understands this, and has labored to bring new plants to the ravaged province. But they have failed to make a dent in the Catholic ghettos, where the jobless rate runs 30 to 40 percent among youths. What jobs there are in a region with an overall unemployment rate near 11 percent are still dominated, especially at the more skilled level, by Protestants.

An Ulster policeman who has lost both legs and an arm is today fighting for his life. The bomb that caught him earlier this week injured five other policemen as well. Tis blast was magnified by the high brick wall around Mackie's, a maker of textile machinery in the heart of a Catholic enclave but with a largely Protestant work force.

Unlike the URA, the vast majority of Ulster's Cahtolics do not want to bomb their way into unity with the overwhelmingly Catholic republic to the south. But their resentment over their plight, their fear and suspicion of British soldiers and a largely Protestant polce force will still provide an uneasy sea for the IRA terrorist-guerrillas.

The Provisionals have been trying to raise funds and sympathy with a new appeal for their 300 colleagues held in a cell block at the Maze Prison in Long Kesh. All have been convicted of crimes-robbery, murder, assault-by judges sitting without jury.

The men refuse to wear prison uniforms or perform prison work. They demand prisoner-of-war status, which Mason steadfastly refuses. In the IRA tradition of self-inflicted wounds, they have refused to wash or use prison lavatories and wear only a blanket in cells that are either too hot or too cold and filthy with excrement, rats and vermin.

Whether appeals for "the men on the blanket" have raised much American money to finance the new campaign is dubious, but the new IRA cells have hardly needed it.

Some 335 bank robberies in Ulster alone this year have yielded $420,000. Bank robberies in the republic have yielded several million dollars mor.

The latest spectacular has forced Scotland Yard to cancel Christmas leaves and pour 2,000 extra police, many armed, into London's West End shopping center. Once again, soldiers armed with automatic rifles, in armored cars and tanks, are patrolling Heathrow Airport.

In time, this wave of bombing is likely to ebb. The police already can claim a triumph of sorts. Ever conscious of headlines, they disclosed that the "Bald Ealge," a bald-headed IRA veteran, was the mastermind directing the English operation.

Late Wednesday, the "Eagle," Cornelius McHugh, was sighted at his isster's Belfast home, telling reporters he had never set foot in Englnad.

But even if genuine arrests are made, anyone who thinks this will stop the IRA's recruiting of embittered young Catholics in Ulter is mistaken.

Oddly enough, a way out of the impasse is beginning to appear for the first time. Thanks to the Common Market, Dublin is enjoying a wave of prosperity that could conceivably wash over the old divisions in the north.

For the last two years, Ireland has been the dazzling growth star of the EEC. Output has gained 6 percent annually, more than twice the rate in the rest of the community. Industrial production has leaped forward by 8.7 percent a year and the traditional high jobless rate is now a shade lower than Ulster's.

The Protestant north has always despised the south as a poor, church-ridden place. But as incomes and urbanization increase, secularization grows too. When Dublin outstrips Belfast-likely before long-northern Protestants may take a new look at the virtues of unity. What IRA bombs are unlikely ever to do, pounds, pence and common sense could some day achieve.