Economics is on the side of a closer relationship between Northern Ireland and the Irish Republic even if politics is not. Such a relationship can come about without sacrificing Northern Ireland's constitutional guarantee that it will remain a part of Britain unless it someday chooses not to. And the need for such a relationship ought to impel the greatest support for strengthened means of Anglo-Irish cooperation - instead of the shortsighted hard-liner opposition to such cooper-ation which was expected and has come to pass.
It was to forestall the worst of such opposition that Prime Ministers Thatcher and FitzGerald chose so carefully among forms of cooperation when they met in London earlier this month. They announced establishment of an Anglo-Irish ''intergovernmental'' council, providing a framework for more frequent and thorough official contacts than the ones already taking place. But the two leaders merely looked toward the possibility of an ''interparliamentary'' council, leaving to the parliaments themselves any decision to seek one. The latter council would formalize existing contacts between British and Irish politicians. Mr. FitzGerald has reportedly been so committed to bringing Northern Irish politicians into Anglo-Irish discussions that he favored more of them in such an interparlia-mentary body than Ulster's population would warrant in proportional terms.
Whether or not the parliaments go for an Anglo-Irish council of their own, politicians on all sides will have to confront the logic of Irish unification short of denying the Northern Irish their mandated right of staying in Britain. The two prime ministers are agreed that only the consent of an Ulster majority - now firmly opposed to leaving Britain - can bring the end of partition. Mrs. Thatcher's Labour Party opposition also agrees, though at its recent conference it favored a long-term approach toward achieving unity by consent rather than simply accepting it if it should come.
The immediate need for reducing strains and divisions on the Irish island is not only to reduce the tragic violence they cause but to revive two Irish economies neither of which is viable on its own. Northern Ireland has been getting by with British help. The currently more successful Irish Republic has been getting by with European Economic Community help. With artificial barriers removed they could both better stand on their own feet.
The urgency of the situation - and the sentiment for change - may be suggested when a British official can publicly describe the Irish border as ''absolutely nonsensical'' in the light of the whole Irish economy. Lord Gowrie, deputy to the secretary of state for Northern Ireland, also went so far as to say that the British government would have to impose a solution if there were not more willingness among Ulster politicians to cooperate in resolving problems.
It will take wisdom on all sides to ensure that cooperation does not become the back-door approach to political unification feared by many in Northern Ireland. Perhaps on down the line a fresh way of looking at the ''British Isles'' is needed. Some have suggested the concept of IONA, Islands of the North Atlantic, with not only Irish and Northern Irish but English, Welsh, and Scottish interests represented in some sort of federal way - protecting the rights of each while joining the strengths of all. Certainly the new official spirit of Anglo-Irish cooperation should foster consideration of all possible avenues of progress in keeping with preservation of the present right to choose.