The US Coast Guard had to put a protective cordon of its ships around the British royal yacht Britannia as it moved into San Diego harbor last weekend. Otherwise a small fleet of Irish sympathizers would have been bumping up against Britannia with their signs saying: ''English: Get out of Ireland.'' As it was, they had to keep 300 yards away - for mutual protection.
In New York City there was a political tempest in the Irish community over the fact that the annual St. Patrick's Day parade is being led by a pro-IRA personality who has proclaimed that the parade this year is a demonstration in support of the IRA.
Former New York Gov. Hugh L. Carey announced that he would boycott the parade because the IRA (Irish Republican Army) is not only an illegal, clandestine terrorist organization in Ulster but also illegal in the Republic of Ireland. The government of Ireland has long since repudiated the IRA and its works and cooperates with British authorities in trying to stamp it out in Ulster.
It was also reported from the Chancery of St. Patrick's Cathedral, seat of Terence Cardinal Cook, Roman Catholic Archbishop of New York, that the Archbishop will probably break immemorial precedent by not reviewing the parade from the steps of St. Patrick's this year.
Back in Ireland the IRA continues its activities which are largely funded by IRA sympathizers in the US. Its most recent was the fatal shooting of Lennie Murphy, a hard-line Protestant leader, in West Belfast on Nov. 16, 1982. The IRA ''took credit.''
What is all this about? Why is the IRA still active in Ulster and still killing people there with support from sympathizers in the US?
The answer is because an injustice done the Irish people by the British 374 years ago still shapes the economic, political, and social pattern of life today in Ulster and still causes a deep sense of resentment.
In Ulster today the descendants of the original Gaelic inhabitants of Ulster are a subordinate third of the population. They are Roman Catholic. They form a pool of cheap labor. They were and still are ''last hired and first fired.''
Ulster is dominated by a Protestant two-thirds of the population whose forebears came to Ireland from northwest England and from the Scottish lowlands beginning in 1609.
With exceptions, of course, it is generally true that Protestants in Ulster to this day own and manage the banks, the factories, most of the land, and most business activity. They own and manage and run and control the politics and the business of the community, because in the year 1609 the British government took away the lands of the great Irish landowners and set up an entirely new and different system of land tenure.
It was called the ''Plantation Plan.'' It provided for three categories of landowners. First were ''undertakers'' who were to be Protestant and who could sublease the individual farms or farm plots only to English or Scottish tenants. Second were ''servitors,'' mainly Scots, who could lease to Irish tenants, but at a higher Crown rent. Third were ''natives,'' i. e., Irish, who could rent to Irish tenants but had to pay double the ''quit rent'' of the ''undertakers'' if they did so.
The plan was, from the British point of view, a great success. English and Scottish Protestants swarmed across the Irish Channel to Ulster. The province was heavily repopulated by Protestants who in the process acquired the preferential political and economic position enjoyed by the Protestants in Ulster to this day.
The condition is known in Ulster as ''Protestant Ascendancy.'' The Protestants still fight to keep it. They continue to be loyal to the British Crown. They do not call or consider themselves to be Irish. They refer to themselves as either British or Ulstermen. Irish in Ulster means Catholic of Gaelic descent. Ulsterman means Protestant descending from the ''Plantation'' of 1609.
This is the ''Ulster problem'' which continues to plague British politics and British-Irish-American relations. It is also a reminder and a warning of how long-lasting can be the results when one people, using superior military power, asserts its ''ascendancy'' over other peoples of a different ethnic and cultural background.
The Ulster ''Plantation'' of 1609 was done by taking land from Gaelic Catholics and parceling it out to English and Scottish Protestants. The Israelis are planting ''settlements'' in West Bank and Gaza by taking land from Arabs and parceling it over to Jewish settlers from Israel. In the process, some Arabs leave, others remain in a condition similar to that suffered by the Irish in the early days of Protestant ''ascendancy.''
The Irish still persist in seeking to undo the ''Plantation'' of 1609. There is no reason to think that the Palestinian Arabs will acquiesce any more willingly than have the Irish. Thus are planted the seeds of future wars.