The idea for the yacht race was brewed in the rainy-day warmth of an Irish bar beside a Maryland harbor. It would be a grand race across the Atlantic, with a pint of Guinness at the start in Annapolis and a few dozen more at race's end in one of Ireland's holy pubs.

That, at least, is the long-range plan. This weekend, the first annual St. Brendan's Cup Regatta stayed comfortably close to home. The race began and ended with pints of stout as promised. But instead of a race across the Atlantic, the sailors went in circles around Chesapeake Bay.

"We have a five-year plan," said James Duffy, a Navy commander of obvious descent who was one of the organizers of the regatta dedicated to elevating the reputation of St. Brendan the Navigator, a sixth-century Irish monk whom Celts claim discovered America 1,000 years before Columbus. "This is what you call the inauguration."

When the ice melts on the Severn River and winter storms become spring squalls, a navy of sailboats hitches a ride out of Annapolis each weekend on the wind. No excuse is needed to sail. And there is never a shortage of races. On any Saturday from April until November, the bay is bedecked with multicolored sails.

Last weekend, for the glory of St. Brendan and an invitation to an Irish party afterward, 130 sailboats raced in 16 classes. Next year, when the race will be run from Boston to Annapolis, there will be fewer with hearts so stout. And in 1984, when organizers plan a trans-Atlantic contest, only the very good, or very foolish, will make the attempt.

"That will be a race," said Desmond Fennell, a college professor who traveled from Galway with half a dozen other Irish representatives for the race. They stood together by the dock and drank by the bar, a congenial reminder that the regatta had a purpose.

"Columbus has a place in the history books," conceded Tadhg O'Sullivan, the ambassador from Ireland to the United States. "He discovered America in his own time. But he needed fine weather for his journey. St. Brendan came over on a rainy Irish day."

While one group of Irishmen waited in the harbor, more were rowing across the mouth of the Severn in boats that looked like a marriage between canoes and Tahitian dugouts. They rowers were members of the Irish Currach Club of Boston, and their boats are descended from the kind Brendan used to cross the Atlantic. In western Ireland, where all of the club members were born, currachs are used to fish during the week and to race on weekends.

"In Ireland, they're still singing songs about races that were won 200 years ago," said Peter Mulkerrin, a roofer with a square jaw, a broad back and a brogue as thick as an Irish mist. A dozen of the club's 35 members made the trip to Annapolis expecting to race against a college rowing team. None would accept the challenge. So the club picked two three-man teams and held its own intramural competition over two miles of choppy water.

The Irish rowers, straining at the oars in damp T-shirts, were a working-class contrast to the teakwood and fiberglass sailboats and their stylishly dressed crews that shared the water and watering holes with them.

"Even if I could afford the clothes, I wouldn't wear them on a bloody boat," said one of the Irish rowers, resting tired muscles in McGarvey's Saloon in Annapolis at the end of Saturday's races. The rowers and the race committee dominated one back room of the bar. In the center of that room, beside a fig tree that reached eight feet above the floor, was Con Howard, the former press secretary for the Irish Embassy in Washington and America's idea of what an Irishman should be.

"The eternal quest for the higher form of life, that is why St. Brendan found America," said Howard, a short man with a stout body, light blue eyes and white hair combed back from a ruddy red face. Howard took upon himself the necessary task of lending some poetry and passion to the occasion. "Every free man has two countries, his own and the United States of America . . . we must follow St. Brendan's mast sailing out forever and ever and ever."

While Howard orated, the committee members talked about future regattas. And the rowers, who would soon return to Boston construction jobs, spoke gamely of competing in the race across the Atlantic.

"Given the right conditions," said Mulkerrin, "we could give it a hell of a try."