As the Asgard II, Ireland's only tall ship, sailed into Washington yesterday on its maiden transatlantic voyage, one mischievous crew member looked up at the Woodrow Wilson Bridge and told his mate, "Quick. Wind down the masts or we'll ram the bridge."

As 15-year-old Carl Coffey vainly looked for a way to bring down the permanently positioned masts, the drawbridge parted and the wooden ship, built in 1981, glided through on its way to the Washington Marina, where it will be docked through Friday.

"I should have known they were up to something," Coffey said, his Dublin accent rich; his blue eyes lively. "They've been pulling stunts since we left."

On March 21, the Asgard sailed out of Irish waters with a 25-member crew, many of them teen-agers with no seagoing experience. It has been an ocean crossing full of pranks, jokes and storytelling -- what the Irish refer to generally as "the crack."

"I don't do it just for the sailing," said 25-year-old Mark Fry, one of the 20 novice sailors whose expenses are paid by the Irish government when they sail the ship on good-will visits to world ports. "I do it for the crack. Oh, it can be mighty sometimes. You can't plan it, you just pick up on what somebody else says or does."

Yesterday, when two U.S. sailors boarded the Asgard to navigate the Potomac, the Asgard crew turned the hoses on them, soaking every inch of their Navy whites.

"The kids have their fun, but they take their jobs serious enough," said Frank G. Traynor, the ship's first officer. "They learn quickly. If they don't, the whole ship is in trouble."

When the Asgard hit force 12 winds, stronger than hurricane gusts, just after they entered the Bay of Biscay in late March, the trainee crew worked together like old hands, Traynor said. Two other ships, a Swiss vessel and a German freighter, sank in that storm. But the Asgard crew of seasick sailors survived, pitching out the water the ship had taken on and wearing harnesses to keep them upright when they were performing chores such as cooking.

Brendan Lyons, a spokesman for the Irish Embassy, said the Irish government will spend more than $305,000 this year to keep the 104-foot ship afloat. It is money well spent, Lyons says, because the Asgard is Ireland's only training vessel, and every year more than 500 youths learn to navigate and steer, clean and cook on board the ship.

"The primary goal is to give the young people experience on a sailing vessel. On a ship you learn quickly how to get along with people," said Lyons. "And when they stop at ports abroad, they are our best ambassadors."

And there are plenty of other ambassadors waiting back home -- one-half of the country's 3.5 million people are under the age of 25.

To show U.S. support for the Asgard's eight-city good-will tour -- which began in Norfolk and ends July 4 in Boston -- House Speaker Thomas P. (Tip) O'Neill plans to give a Capitol Hill party for the crew.

While the 93-ton brigantine is docked at the Washington Marina, Coffey said he plans to see "two things I've heard a lot about:" the White House and the FBI headquarters.

Whether he feels like a good-will ambassador or not, Coffey says he knows many Irish legends well, including the one that inspired the trip. And it won't take much urging to get him to tell the story of St. Brendan, a 6th century Irish monk who the Irish say discovered America well before Christopher Columbus.

"It wasn't just by a few years that St. Brendan beat him over here," Coffey said aboard ship yesterday. "It was 900 years."