LONDON — ONE year after the Irish Republican Army (IRA) declared a cease-fire in Northern Ireland, its political leaders appear convinced the White House holds the key to rescuing the faltering peace process. Yet they may have to wait until late November, when President Clinton visits Belfast, before that key can be turned. Meanwhile, peace appears shaky as communal enmities and sporadic street violence overshadow and threaten a renewal of the terrorism that over 25 years, until Aug. 31 last year, had claimed 3,200 lives. Today the politics of Northern Ireland look like a classic case of an irresistible force hitting an immovable object. Britain and Sinn Fein, the political wing of the IRA, are deadlocked on whether - and when - terrorist arms should be given up. On Aug. 27 London again insisted that the IRA must first agree to begin handing in their weapons before they can take part in talks on Northern Ireland's future. But Gerry Adams, leader of Sinn Fein, the IRA's political wing, is adamant that the IRA should hold on to their weapons and explosives until talks begin - and he thinks Mr. Clinton agrees with him. After three hours of talks Aug. 28 with the prime minister of the Irish Republic, John Bruton, Mr. Adams repeated calls for early talks that include all parties. The Sinn Fein leader said British insistence that arms be handed in before talks are held was ''a formula for disaster.'' To back up their belief that the White House shares their views, Sinn Fein sources cite a leaked letter from Clinton to former US Rep. Bruce Morrison, a key figure in the Irish-American lobby and the president's special envoy on Northern Ireland. In it Clinton says he favors discussing the decommissioning of IRA arms during all-party talks, not before them. The text of Clinton's letter was published in the Dublin Sunday Business Post newspaper Aug. 27. . 'Clinton is our ally' A Sinn Fein representative who requested anonymity said: ''It was Clinton who in the teeth of British resistance allowed Gerry [Adams] to visit the US. He is right behind the campaign to boost investment in Northern Ireland. Now it is clear he is against current British policy on arms handovers. Clinton is our ally.'' Sinn Fein is also showing close interest in a White House idea that could break the logjam: setting up an international commission to supervise arms handovers by the IRA as well as unionist paramilitary groups, which want to keep British rule in the province. Sinn Fein chairman Mitchel McLaughlin said on Aug. 26 the organization would ''look very, very carefully and seriously'' at the commission proposal. But he added that Britain must first drop its insistence that arms handovers should precede all-party talks. In London, a senior British official conceded that the commission idea was ''worth considering.'' But he would not agree to a suggestion that the idea offered a compromise Britain ought to be able to accept. After his talks with British and Irish officials earlier this year, Mr. Morrison, the former Congressman, was reported as suggesting that the proposed international commission could hold discussions on arms that would run parallel to talks between the parties in Northern Ireland. Albert Reynolds, the former Irish premier who along with Prime Minister John Major helped to launch the peace process last year, on Aug. 27 urged Britain to agree to all-party talks without preconditions. But Michael Ancram, deputy Northern Ireland secretary, said London was not prepared to conduct negotiations ''under the shadow of a gun.'' Dublin then said it might decide to stay away from a British-Irish summit planned for Sept. 6, saying Mr. Major and Mr. Bruton were too far apart for a meeting to be useful. Muddying the political waters still further, a new obstacle to progress appeared virtually on the eve of the cease-fire anniversary: James Molyneaux, leader of Northern Ireland's dominant Ulster Unionist Party (UUP), announced his immediate resignation. A British government source said his sudden departure meant little progress could be expected until the UUP had chosen a new leader. There appeared to be an emerging consensus that Molyneaux's successor would come under heavy pressure from unionists, who want Northern Ireland to stay part of the United Kingdom, to adopt a tougher negotiating stance. The story of the past 12 months has been one of high initial hopes steadily gnawed at by mutual distrust between the two Northern Ireland communities. When the IRA declared a unilateral and unconditional cease-fire a year ago, the move triggered a matching declaration in mid-October by the main unionist guerrilla groups. In February, the London and Dublin governments published a ''framework document'' offering outline proposals for the future government of Northern Ireland. This was followed by informal contacts between Sinn Fein and London, and a committee of experts has been holding technical talks about arms handovers. In Northern Ireland itself, the only violent death even vaguely associated with the long-running ''troubles'' has been the murder of a post office worker during a robbery. It is not believed to have been politically motivated. Since the truce took effect, British troops in Northern Ireland have taken a far more relaxed attitude. In most areas, police now patrol without back-up from British soldiers. British troops no longer wear battle gear. Vehicle checkpoints barely exist. Roadblocks have been dismantled. London has begun moving IRA prisoners held in England to prisons in Northern Ireland, where they can be closer to their families. These moves have helped to stoke business confidence in Northern Ireland. House prices have been rising. Tourists and shoppers have begun flocking to Belfast as word spread that wandering the streets of the Northern Ireland capital and other towns was no longer dangerous. Sir Patrick Mayhew, the Northern Ireland secretary, justifies the softer security approach with the argument that confidence-building measures improve the political atmosphere. But he and Major have had to tread carefully, since every concession to the IRA is likely to be seen by pro-British unionists as a betrayal. Last week, in a bid to jump-start the stalled peace process, Mayhew announced that Northern Ireland's paramilitary prisoners would get a 50 percent reduction of their sentences. Adams, however, rejected the move as ''too little, too late'' and repeated his demand to be allowed to join in all-party talks now. ''It is a disgrace that Britain by its policies is making talks impossible,'' he declared. A feature of the current impasse is that broad popular support does appear to exist for a parallel approach to arms decommissioning and the start of all-party talks. A survey in Dublin's Sunday Tribune newspaper on Aug. 27 polling citizens of Northern Ireland showed 64 percent backing for the two processes to run together. Among Protestants, 57 percent said the unionist political parties should hold discussions with Dublin. But hopes that the cease-fire will be permanent are beginning to fray. A poll last week by the Belfast Irish News showed that 46 percent believe there will be a return to violence by the IRA - up 2 percent since the same question was asked last February. Paramilitary 'policing' Mary Holland, a long-time analyst of Irish politics, says the violence accompanying the summer ''marching season,'' when Protestants ritually commemorate historic victories over Catholics, has heightened tensions and lowered expectations of a lasting peace. The marching season ended at the weekend with scuffles in several towns between Protestants and Catholics. Holland notes also that although terrorist murders have ceased, ''punishment beatings'' by IRA and unionist paramilitary groups to control their own turf have not. The beatings and sporadic communal clashes during the marching season are reminders of how easily the opportunity for a lasting peace could be lost, she says. As the search for a way forward continues, British government officials are refusing to comment on the role Clinton may decide he wants to play. The British government characterizes his visit in late November as a normal diplomatic event. But Clinton's decision to meet Sinn Fein leader Adams at the White House last March in defiance of Prime Minister John Major's wishes still rankles, just as Mr. Major's refusal to speak with the president for some weeks afterward attracts tart comments from American officials. Major is well aware that, for Clinton, the Irish question is an important domestic issue. But just as Adams and the Irish government hope Clinton's visit can prompt a settlement, Major and unionists fear White House pressure to make big concessions. Mr. Reynolds pinpointed Aug. 27 the moral pressures Britain is likely to face as Clinton's visit nears. ''One would have thought that people would apply common sense and pragmatism,'' the former premier said. ''After all, this process is about saving life, not saving face,'' he added.