Since last weekend, the streets of Northern Ireland and the newspapers and television screens of the rest of Britain have once again been full of sectarian marches and rallies, rioting, mass arrests, raids and disarming of bombs by security forces. It all marked a macabre anniversary.

Ten years ago this week, after several days of battle between rioting Catholics and equally violent Protestant police and reservists in Northern Ireland an emergency British Army peacekeeping force was sent there "to help out the police for a few weeks."

Today, there are still 13,000 British troops in Ulster. The decade of sectarian warfare has claimed the lives of 301 British soldiers, 222 Ulster police officers and reservists, and 1,413 civilian men, women and children. Nearly 21,000 people have been injured. Thousands of buildings have been damaged by 6,500 bombings.

The taxpayers of the rest of Britian have spent more than$5 million a day to support the troops and other security measures in Northern Ireland and to help its dying economy and jobless families with industrial subsidies and welfare payments.

Yet unemployment in Ulster is twice as high as in the rest of Britian, a quarter of the families live below Britian's official poverty line, and a third of the housing is substandard. Furthermore, continuing economic stagnation in Britian and Prime Minister Margaret Thatcher's across the board government spending cuts are expected to make the economy of Northern Ireland even worse.

Despite generally efficient British rule an overall lowering of the violence since the worst years in the mid 1970s and the eerie normality with which the majority of Ulster's Protestants and Catholics live among the soldiers, checkpoints, bombed out building and shadowy danger of death, there is as little optimism as ever about the future.

The scale of the past week's marches, rallies and rioting was relatively small. But soldiers fired rubber bullets on several occasions to stop violent crowds, and an apparent Provisional Irish Republican Army anniversary plot to blow up a military patrol was foiled when troops found and defused a bomb.

The Provisional IRA has come back from almost being squashed under the thumb of the increasingly sophisticated security forces. It is now a leaner, more secretive and professional hard core of a few hundred terrorists who have been more efficient and ruthless in killing British soldiers, Ulster police officers and Protestant reservists this year, while attacking fewer civilian targets.

"There is no doubt that, until the end of 1978, violence was diminishing from the high level of two years earlier," Thatcher's Northern Ireland secretary, Humphrey Atkins, told Parliament last month. "Substantial successes had been achieved by the security forces against the terrorists and their level of operations decreased.

"It is clear, however, that during that period [members of] the Provisional IRA were regrouping, retraining, reequipping themselves and rethinking their future tactics. The first six months of this year have shown a marked increase in the level of terrorism and have demonstrated that we are up against a more professional enemy organized on a system of self-contained, close knit cells, which makes it difficult to gather information."

The IRA has concentrated on military targets because so much of the Catholic population had been alienated by the killing of noncombatants.

The Provisionals have plenty of money and guns smuggled in from foreign sources. They also appear to have contacts with worldwide terrorist groups. A British diplomat was assassinated in The Hague earlier this year. An IRA splinter group, the Irish National Liberation Army, assassinated prominent Conservative member of Parliament Airey Neave just outside the House of Commons with a car bomb in April.

Last Sunday a handful of masked and heavily armed IRA gunmen surfaced dramatically for publicity pictures during a "Brits out" Catholic rally against the British occupation. The security forces retaliated with mass raids and arrests of IRA suspects in Catholic neighborhoods of Belfast.

A secret British government assessment of the Northern Ireland situation, leaked earlier this year by someone who found it in a batch of stolen mail, concluded that the IRA and the security forces were still at a standoff that would necessitate the presence of British troops and direct British rule in Ulster for at least five more years.

There are signs, however, that political calm increasingly is giving way to dangerous polarization.

Reacting to recent IRA shows of bravado, the long dormant Protestant Ulster Defense Association has announced that it might return to paramilitary activity and try to "eliminate the leadership of the Provisional IRA," a threat that raised the specter of Protestant gangs who retaliated against the IRA by murdering large numbers of Catholics in the mid 1970s.

The Rev. Ian Paisley, Ulster's most vitriolic anti Catholic leader, has bounced back from the political embarrassment of the abortive Protestant general strike he led in 1977 to win reelection to Parliament in May and an Ulster seat in the European Parliament election a month later, Paisley has vowed to work from the inside to wreck the 'european Community, which he sees as "the Roman Catholic superstate" that would merge Ulster with the Irish Repubic.

Moderate Protestant politicians in Northern Ireland won only safe seats to Westminister and did particularly badly in the Common Market election. The Nonsectarian Alliance Party, once Britain's hope for a political settlement in Ulster, finished well out of the running in both elections. The Peace People movement begun by anti IRA Catholics in 1976 virtually has died out.

As frustration with an increasingly polarized status quo in Ulster has increased, the British government has come under increasing pressure to do more to find a solution to the Northern Ireland problem.

Paisley and his followers want Britain to return government in Northern Ireland to the Protestant majority, with its own Parliament at Stormont Castle in Belfast, and fight an all out war against the IRA. More moderate Protestant leaders want a new Protestant run layer of local government between the British Parliament and existing city and town governments.

Political leaders of Ulster's Catholic minority, leading Irish American politicians in the United States and the government of the Republic of Ireland across the border all want Britain to negotiate a settlement that eventually would remove the British troops and unify Ulster with Dublin.

The British have sought for several years to negotiate a settlement under which the Protestants and Catholics would share power in a regional home rule government as part of Britain. Ulster Secretary Atkins is sounding out politicans on both sides in Norther Ireland about this.

Atkins apparently was chosen for his difficult job, after the death of Neave, because of his steadiness, patience and persuasiveness as the Conservaties' chief whip in Commons.

There is concern here, however, that Atkins may be keeping too low a profile. He has been criticized strongly for vacationing in Tunisia during this past week's tense 10th anniversary of the deployment of British troops in Ulster.

Ireland's opposition leader, Garret FitzGerald, has proposed the creation of a loose confederation between the north and south in which foreign and economic matters would be conducted jointly, and everything else would remain, at the beginning, in the hands of separate governments in Belfast and Dublin. This plan offers Ulster a chance to share in the rapid economic growth Ireland has enjoyed since joining the Common Market. It also would fulfill Ian Paisley's fears that Ulster might be seen to have more in common economically with Ireland than with the rest of Britian.

While the British government has greeted FitzGerals's proposal with silence, several influential journalists have urged that it at least be considered for discussion. Without embracing this particular plan, the Labor Party's Northern Ireland secretary, Merlyn Rees, this week urged Thatcher's Conservative government to reopen a meaningful dialogue on Northern Ireland with Dublin, while trying to find common ground with the two sides in Ulster.