London — In the three capital cities that stare at one another across the bitter divides of Anglo-Irish history, a new phase is opening in the long effort to make peace.
No one expects progress soon. London, Dublin, and Belfast agree that only the tone, rather than the substance, of Irish relations with London has been changed by the apparent victory of intellectual, voluble, Garret FitzGerald of the Fine Gael Party over Charles Haughey and the Fianna Fail.
The victory creates some opportunities: Mr. FitzGerald spoke Nov. 27 of the urgency of finding solutions to the problems of Northern Ireland.
Yet it also brings a new set of anxieties for the majority Protestants in Belfast. Mr. FitzGerald's moderation and determination to float new ideas are already causing Protestants such as Harold McCusker of the Official Unionist Party to dig in their heels and reject FitzGerald efforts to make the south more acceptable to the north.
Conversations on both sides of the Irish Sea in recent days indicate that any form of united or federated Ireland, and any hope of federated or other links between that Ireland and Britain, are five years away at the very least. Bitterness and sectarian suspicion run very deep.
Mr. FitzGerald wants a ''complete and radical rethinking of British policy . . . if the situation is to be retrieved from a drift towards chaos,'' as he said in a major speech Nov. 18.
The core of his own approach is to calm Protestant fears by altering the Irish Constitution and presenting a more acceptable, moderate, and less stridently Roman Catholic image.
As it now stands, the Constitution pledges Ireland to support all the teachings of the Roman Catholic Church and claims jurisdiction over all of Ireland, north and south.
While briefly in power last year, Mr. FitzGerald threw out ideas to change this language. During the recent campaign he introduced equally controversial new elements such as an all-Ireland judicial and police system.
Predictably, that upset Protestants in the north and die-hard Catholics in the south. The south wants no armed British police on its territory, for example.
Mr. FitzGerald has also said he hopes to launch new talks with British Prime Minister Margaret Thatcher next year. He will also focus new attention on Anglo-Irish talks begun at a summit between Mrs. Thatcher and Mr. Haughey two years ago. They have been continuing steadily on security, energy, tourism, agriculture, water supplies, and other cross-border issues.