Clinton Leaves on European Visit That’s Assumed New Import Since Its Planning : Diplomacy: Wooing Catholic voters was aim of Irish visit. Now peace in Ulster is on front burner. Bosnia affects entire trip.

President Clinton left Tuesday for a trip across Europe focusing on U.S. efforts to make peace on two of the continent’s ancient battlegrounds: Northern Ireland and the Balkans.

“The United States is proud to support the peacemakers--in Northern Ireland, the Middle East, Bosnia and throughout the world,” Clinton said as he boarded Air Force One at Andrews Air Force Base. “Those who stand up for peace will have the United States standing with them.”

The President’s five-day journey was originally designed as a sentimental visit to his ancestral homeland, Ireland, that would produce handsome television pictures for a presidential campaign year.

But with a new peace agreement for Bosnia-Herzegovina that calls on the United States to provide about 20,000 troops, and a new initiative for Northern Ireland announced on the eve of Clinton’s arrival by the governments of Britain and Ireland, the trip has already turned into a more serious diplomatic mission.

On Northern Ireland, British officials want Clinton to press the leaders of Sinn Fein, the political wing of the Irish Republican Army, to agree to give up their weapons in an internationally supervised process.

Clinton has considerable influence with Sinn Fein because he has helped bring the group into negotiations, in part by allowing its leader, Gerry Adams, to make several official visits to the United States.

The President gave the new Anglo-Irish agreement a strong endorsement Tuesday and called on all factions in Northern Ireland to accept it.

“This is an opportunity to begin a dialogue in which all views are presented and all can be heard,” he said.

On Bosnia, the President will be assuring European leaders that he is determined to send the promised U.S. troops to the nation despite criticism from Congress--and, in turn, he will be seeking help from the Europeans in persuading Congress that the deployment is a good idea.

Clinton is scheduled to spend today in London with British Prime Minister John Major, talking about both issues.

On Thursday and Friday, he is scheduled to join a large delegation of prominent Irish Americans for stops in the British-ruled province of Northern Ireland and the Republic of Ireland in the south of the island.

Among the President’s guests on the journey are Los Angeles Mayor Richard J. Riordan, Chicago Mayor Richard M. Daley and Maryland Lt. Gov. Kathleen Kennedy Townsend, a daughter of the late Sen. Robert F. Kennedy.

But Clinton has a more valid reason than most U.S. politicians for spending time in Ireland: For three years, he has been working to encourage peace among the British government and warring Protestant and Roman Catholic extremists in Northern Ireland.

White House aides said credit for the new agreement should go to Major and Irish Prime Minister John Bruton--but they added that Clinton’s impending visit gave the two leaders a deadline to work against.

Indeed, only last week U.S. officials charged that the British government was dragging its feet in the talks because some Major aides disliked the idea of Clinton collecting more credit for putting pressure on London.

But the President may not want to lean too hard on Major over Ireland, because the British prime minister is one of his most important allies on the front-burner issue of making peace in Bosnia. Clinton plans to send the U.S. troops to the former Yugoslav republic to enforce a peace agreement initialed in Dayton, Ohio, last week; Major has promised thousands of British troops as well.

The pressing business of Bosnia delayed Clinton’s departure for London by a day and also prompted him to scrub a planned day of golf at Ballybunion, a spectacular course along the estuary of the River Shannon. Instead, the President will visit U.S. Army units slated for duty in Bosnia at Smith Barracks in Baumholder, Germany, on Saturday.

Nevertheless, Clinton will still have some opportunities to make domestic political hay out of his time in Ireland, even though he has no ancestral village to return to. Irish genealogists tried to find the President’s Hibernian roots through the lineage of his late mother, who was born Virginia Cassidy, but failed.

An estimated 44 million Americans claim some Irish ancestry, most of them Catholics--and Catholics have turned out to be a key swing vote in recent presidential elections. Once solidly Democratic, Catholics voted for Republican Ronald Reagan in both 1980 and 1984, split narrowly between George Bush and Michael S. Dukakis in 1988, and went for Clinton by a wide margin in 1992.

In the 1994 congressional election, a majority of Catholics voted for Republican candidates for the first time in history--meaning that many who voted for Clinton in 1992 are now disenchanted. Democratic strategists say those voters are one key target of the President’s 1996 reelection campaign.

Clinton’s Irish American guests on the trip include important opinion leaders, potential campaign donors and even two novelists: William Kennedy, who won the Pulitzer Prize for “Ironweed,” his gritty novel of working-class life in Albany, N.Y., and Pat Conroy, whose potboilers such as “The Prince of Tides” and “The Great Santini” have achieved less lofty critical acclaim but more jaw-dropping commercial and cinematic success.

The guest list also includes Mayor Daley’s younger brother William, a behind-the-scenes Democratic powerbroker; Pittsburgh Mayor Thomas J. Murphy Jr.; both the outgoing president of the AFL-CIO, Thomas R. Donahue, and his newly elected successor, John J. Sweeney, who grew up in adjoining Irish American neighborhoods in the Bronx, and Clinton’s top campaign fund-raiser, Terrence R. McAuliffe.

Riordan’s chief of staff said the Los Angeles mayor, a Republican who has cultivated a sometime alliance with Clinton, decided to go on the trip for practical and sentimental reasons.

“It’s more than a trip to the mayor’s ancestral homeland,” Riordan aide Robin Kramer said. “He intends to promote Los Angeles.”

Times staff writer Marc Lacey contributed to this report.