BELFAST, AUG. 31 -- The Irish Republican Army today announced a "complete cessation" of its violent campaign to unite Ireland, providing the clearest opening in many years for a negotiated settlement of Northern Ireland's 25-year-old civil war.

The IRA, which has been fighting to end British rule in the religiously divided province, said in a statement that its decision marks a "historic crossroads" and offers "a new opportunity" to resolve a conflict that has claimed more than 3,000 lives and trapped the region in a cycle of violence, despair and economic stagnation since 1969.

The British, Irish and U.S. governments all welcomed the IRA announcement, saying they hope it means the beginning of the end of civil strife in Northern Ireland. But Britain also complained that the IRA statement did not go far enough because it failed to make plain if the announced cease-fire, set to begin at midnight, is to be permanent.

Nonetheless, British Prime Minister John Major called the decision "a very great chance for peace." President Clinton said the announcement "can mark the beginning of a new era that holds the promise of peace for all the people of Northern Ireland."

Major said that if the opportunity offered by the IRA announcement is to be realized, "we need to be clear that this is indeed intended to be a permanent renunciation of violence," an assessment echoed by other senior British officials.

Reaction from Northern Ireland's Protestant majority -- which seeks to remain part of Britain and opposes the IRA goal of reuniting the North with the mainly Catholic Republic of Ireland -- ranged from cautious optimism to howls of disbelief that the IRA truly intends to pursue a peaceful path.

The skeptical Protestant response dampened a mood of euphoria that swept through many quarters of this troubled province after the IRA declaration early today.

By evening, political leaders on all sides of the conflict found themselves drawn into a tortured debate over whether the IRA's proclaimed "complete cessation" of violence is permanent.

The point is crucial because London and Dublin stated last December, in a declaration of principles on bringing peace to the province, that the outlawed IRA's legal political wing, Sinn Fein, could join comprehensive, all-party talks on the future of Northern Ireland only after a permanent cease-fire had been announced and adhered to for three months.

British officials said the three-month waiting period would not begin until Sinn Fein makes clear that the IRA has halted its campaign of violence for good. "The moment I am clear in my mind that this is a permanent end to violence, then the clock starts ticking," Major said.

Without such clarity, there would be an unacceptable "implied threat of violence" hanging over the contemplated all-party talks, said Sir Patrick Mayhew, Britain's cabinet secretary for Northern Ireland.

British officials said there is no need for the IRA or Sinn Fein to make a formal, precisely worded declaration that the announced cease-fire is to be permanent. But Sinn Fein somehow has to make it plain to people in Northern Ireland that a permanent cease-fire is the intent, they said.

Sinn Fein President Gerry Adams acknowledged at a news conference that the IRA statement did not explicitly say how long the cease-fire would last. But he added: "Looking at it from a Sinn Fein perspective, we want to see a permanent peace."

For his part, Irish Prime Minister Albert Reynolds said he is convinced that IRA violence is over for good and that all-party talks on Northern Ireland's future could begin soon, as contemplated by a joint British-Irish agreement -- called the Downing Street Declaration -- that was signed last December. Still, Reynolds added, "Peace will take time."

If debate about the meaning of the IRA cease-fire does not immediately bog down the peace process, several tracks of negotiation are likely over the next weeks and months, British and Irish officials said.

Within days, British and Irish representatives will meet to review the IRA announcement, officials said. If the cease-fire holds, Ireland plans talks that are likely to bring together Catholic-oriented parties in the Republic of Ireland and Northern Ireland.

In several months, if all goes well, the toughest bargaining would begin, likely involving Britain, Ireland, Sinn Fein, anti-IRA Catholic groups in Northern Ireland and perhaps some moderate Protestant parties. How wide an agreement might be reached is far from clear; one popular but hard-line Protestant political leader, the Rev. Ian Paisley, has declared repeatedly that he will never sit at the negotiating table with Sinn Fein.

Along this precarious negotiating path, a number of issues loom as potentially serious obstacles to a permanent settlement. They include:

Demographic gridlock. About 60 percent of Northern Ireland's population is Protestant. Opinion polls suggest that, at present, nearly all of them want to remain part of Britain.

A bedrock principle of British and Irish support for the unfolding peace process is that nothing will change in Northern Ireland unless a majority of the province agrees to it in a democratic vote.

Protestants in Northern Ireland see this as their right to self-determination, but Sinn Fein and the IRA denounce it as an unacceptable "Protestant veto" over a united Ireland. "The Unionist veto must be ended," Adams declared again today.

Has this republican view really changed? Sinn Fein now says it wants Britain to try to persuade Protestants to vote to join a united Ireland. Republicans pledge to respect Protestant traditions in this new, united Ireland created by referendum.

But many Protestants fear that at the end of all the talking, if they choose democratically to remain with Britain, the IRA will simply pick up its weapons and start all over again.

Protestant paramilitary groups. Most of the killings in Northern Ireland during the past few years have been carried out not by the IRA, but by its Protestant rivals, called loyalists. Many fear that a cycle of violence could be reignited quickly if Protestant groups continue with violence while the IRA has laid down its arms.

The Combined Loyalist Military Command, an umbrella organization of key Protestant paramilitary units, issued a terse statement today in response to the IRA cease-fire declaration. It said it awaited Britain's detailed views on the province's future and wished "to make it clear that we will not be dancing to the pan-nationalist tune."

Security in the streets. Sinn Fein's most immediate demand is for a visible reduction of Britain's military presence on Northern Ireland streets, particularly in the IRA's Catholic strongholds. Britain has recently offered hints that it will draw its 18,000-strong army back to its barracks gradually if the cease-fire holds. But if the British military pulls back, who will provide security for the province's Protestant-dominated police and for Catholic neighborhoods?

In reaction to the cease-fire announcement, local radio talk show switchboards brimmed with callers whose voices alternated between soaring tones of hope that peace negotiations might finally succeed and skeptical warnings that it is far too early to believe that a lasting settlement is at hand.

Pessimists offered stern reminders that during the last prolonged IRA cease-fire, in 1975, more than 200 people died in continuing violence and the peace ultimately broke down amid vicious splits among parties to the conflict.

Optimists argued that the lessons of history have been learned, that all sides are altogether weary of war and that the peace process today has much broader political and institutional backing than it had two decades ago.

Past cease-fires called by the Irish Republican Army:

1972: Attacks halt June 26 while representatives hold talks in London. British official says IRA made impossible demands. Truce ends July 9.

1974: Brief truce in late December during talks with British officials.

1975: Indefinite suspension of attacks Feb. 9. Despite violence by pro-British Protestants and continued IRA activity, cease-fire generally holds until Sept. 22.

1990: Three-day truce observed over Christmas for the first time in 15 years. Similar break called every succeeding year.

1994: Three-day cease-fire during Easter, as IRA seeks gesture from the British government. British and Irish governments reject brief halt as inadequate.

SOURCE: The Associated Press