Irish Prime Minister Charles Haughey's message at the White House luncheon to honor St. Patrick's memory was more akin to the damp, dispiriting weather on the day than to the ray of sunshine so lovingly ascribed to it by Colman McCarthy ("Finally a Leader of Ireland Urges: 'Brits Out,'" op-ed, March 27).

"Blarney," roughly translated, means nonsense. And it wasn't just blarney but blarney of a fanciful and romantic kind that McCarthy served up. Blarney, however, was not what Haughey was offering. Unlike many Irish Americans, he knows the import of his message conveyed to over 1 million Protestants and Roman Catholics in Northern Ireland.

"Brits Out" to them doesn't mean British troops out or British government out: it means they are out--that there is no place for them on the island of Ireland unless they surrender to Gaelic Catholic nationalism. Haughey apparently has no interest in removing that fear as an essential precondition to establishing better relationships between the two parts of Ireland. He intends to reinforce it.

Haughey believes that between himself and the British government, and over the heads of the people of Northern Ireland, he can hammer out a program that will lever Northern Ireland out of the United Kingdom and into a united Ireland. And if he can get a little help from his friends in the U.S. administration and Congress, so much the better.

Contrary to McCarthy's suggestions, the only pressure group needed in the United States is one that recognizes the need to stop gun-running from the States, one that understands that dollars placed in collection boxes in New York, Boston and even Washington are ultimately used to kill people in Northern Ireland or, alternatively, to give killers a life style and affluence they would never attain by honest effort.

Since I became a member of Parliament for Armash, 208 of my constituents have met their deaths at the hands of the Provisional IRA. Most of them were Protestants, but over 20 of them were Catholics, co-religionists of their killers. None of them enjoyed the privilege of a trial or a defense. None of them will ever enjoy an amnesty or release. Prison gates will eventually open, but graves do not.

To compound their agony, the people I represent know that the perpetrators of murder in our society enjoy sanctuary across the border in Haughey's Republic. Over 600 terrorist suspects are currently "on the run" in the Republic. For as long as they freely walk the streets of Dublin, we cannot but regard Haughey and the Republic as hostile. True, Haughey has uttered some fine words, but I fear they are merely part of the ritual--they've never been accompanied by action.

Fortunately, President Reagan didn't fall for the Haughey line. Someone in the administration knows a little bit more about the complexity of the problem and about human nature than Haughey believed. Or did he really want anyone to take him at his word? There are many who suspect that "Brits Out" is really an excuse for a real policy, and is simply a useful diversion to take the minds of the electorate in the Republic off what should be its most pressing priority: the virtual bankruptcy of the economy.

Whatever the reason for Haughey's behavior and however McCarthy chooses to describe it, the weather forecast for Ireland will continue to threaten disaster, not sunshine, so long as belligerence takes the place of neighborliness, and coercion is preferred to consent.