PRESIDENT Reagan has been urged by Charles Haughey, leader of Fianna Fail - the main opposition party in Ireland - to make a significant and historic statement on US policy toward Ireland during the President's visit in June. Mr. Haughey suggests that the President should tell both houses of the Irish parliament during the keynote speech of his short tour that ''henceforth the United States will include the historic unity of Ireland as a major objective of her foreign policy.'' Such a statement, Mr. Haughey says, would be one of those ''noble and generous acts which have happened from time to time in American history.''
It would also be the final tribute, he suggests, to the ''enormous contribution'' by the ancestors of some 40 million Irish-Americans in helping to build America, and it would also be a recognition of the part played by Irish-Americans in the political life of the US.
So much for Irish rhetoric. Mr. Haughey's appeal was made on March 31 at the annual general meeting of his party in Dublin and was calculated to win the approval of the rank-and-file members of Fianna Fail, who regard themselves as the true heirs of Irish republicanism. But it is doubtful if such an appeal will be taken up.
Political common sense would suggest that the President will confine himself to a message of goodwill in Ireland and that he will decline to become involved in a problem that is of concern to two of America's international allies, namely Britain and Ireland. The US is rather like a friend of two people involved in a difficult situation, like an unhappy marriage. To intervene is to risk losing the friendship of the one or the other. The wise friend will express concern but will avoid the flying crockery and the interminable arguments.
A US intervention on Northern Ireland would put immense strain on old friendships and create further problems for an American administration that has more than enough problems already. However, the US can be of continuing assistance in helping to find a peaceful solution in Ireland in two ways - by using every means possible to stop the flow of money to buy arms for the paramilitaries in Ireland, and by encouraging Americans to take an informed interest in the Ireland and Northern Ireland of today, rather than the myths and misrepresentations of the past.
A few weeks ago I spent nearly a fortnight in the United States to learn more about American attitudes to Ireland. My visit began in New York and extended to the West Coast and I found three distinct attitudes.
There is a large group of Americans who do not understand what is happening in Ireland and who do not wish to think about it. They find it incredible that people with the same ethnic background should seem to be engaged in a war over 17th-century religion. And so they simply switch off.
Another group consists of the Irish-Americans, many of whom have fixed views. In many cases their concept of Ireland has not changed since they or their forebears emigrated to America. Many minds snapped shut decades ago and are unlikely to open now. The best that a nonviolent visitor from Ireland can do is to try to convince them that support for organizations rooted in violence is not the answer to the problem.
The third group consists of Americans - many with Irish roots - who are prepared to listen to both sides of the problem and who are prepared to learn. However, it is still difficult for a Northern Ireland citizen to persuade them that Ulster is not simply a colonial problem.
Once they are told that around 1 million Ulster people actually are British and want to remain British, the impartial American audience begins to realize that the situation in Northern Ireland is not necessarily as simple as it seems from afar.
From this side of the Atlantic there are no simple solutions. It is not a matter of a British withdrawal or of US backing for Irish unity. The best hope for the future lies in a long, unspectacular, and extremely difficult process of persuasion that the people of Ireland and of the British Isles have a great deal in common, that they have more in common as Europeans and as human beings than that which divides, and that violence will only exacerbate the existing problems.
No doubt President Reagan and his advisers will be mindful of the complexities of Irish politics during their visit. President Reagan will be warmly welcomed not only for himself but also as the symbol of the close ties between the US and Ireland. The President will be anxious to underline those ties, but on the thorny question of Irish unity he would be well advised to follow the wise old Irish maxim: ''Whatever you say, say nothing.''