By Ian Graham

BELFAST (Reuters) - Hillary Clinton will travel to Northern Ireland on Friday for one of her last foreign trips as U.S. Secretary of State, lending support to a fragile peace that was one of the greatest successes of her husband's presidency.

She visits a province transformed by the 1998 peace agreement but still riven by sectarian loyalties, with a prison officer shot dead by nationalist militants last month and unionist protesters rioting over the removal of a British flag.

The visit will also be a reminder of the huge popularity of the Clintons in Ireland, a potential asset in attracting the Irish-American vote if Hillary decided to run for the U.S. presidency in 2016.

The province has suffered one of the world's worst property market crashes and its leaders are hoping for the kind of U.S. foreign investment that has transformed the rest of Ireland.

"Our need is more economic now than political," said Reg Empey, Chairman of the Ulster Unionist Party, who was a senior figure in the peace process.

"But we also have to be aware that there is still a degree of volatility ... and in those circumstances I think we should make sure we keep the relationship going."

PEACE PROCESS

Hillary Clinton travelled to Northern Ireland several times in the mid-1990s while her husband helped broker the 1998 Good Friday peace accord, his hands-on approach widely recognized as crucial at moments when the agreement looked like crumbling.

Bill Clinton's work helped win over the Irish vote during his re-election campaign in 1996 and his popularity among Irish Americans could rub off on Hillary should she decide to run for office.

"I'm not making the assumption that Hillary's career as a front-line politician has ended," Empey said. "If you have someone in the White House with good working knowledge of the North and the peace process, that can only be good for us."

Clinton on Thursday told journalists in Dublin she was "too focused on what I'm doing" to think about a run for the presidency.

She declined to comment on U.S. newspaper reports that her husband may be appointed as Washington's next ambassador to the Republic of Ireland.

PERSONAL TIES

As first lady, Clinton lent support to pro-peace women's groups in Northern Ireland and visited people injured in the 1998 Omagh bombing, the deadliest attack in three decades of violence commonly known as the "Troubles".

At least 3,600 people were killed during that time as Catholic nationalists seeking union with Ireland fought British security forces and mainly Protestant Loyalists determined to remain part of the United Kingdom.

"The lessons learned here in Ireland about how to build peace could be of great use to other peoples and nations," Clinton said in a speech in Dublin on Thursday in which she recalled a meeting between Catholic and Protestant women in Belfast in the 1990s, with one of whom she remains friends.

"There are so many more ties that bind us than divide us, and that is what has motivated me over many years now," she said.

SHAKY PEACE

The 1998 peace has mostly held, although militant nationalists have stepped up attacks in recent years, shooting dead a prison officer on his way to work last month.

Clashes involving nationalists, loyalists and police still break out in Belfast several times a year.

Riots have broken out twice this week after nationalist councilors voted to take down the British flag atop Belfast City Hall.

"The people who are managing the low level (of violence) at the moment could make a mistake and suddenly we would have an awful lot of trouble," said Malachi O'Doherty, a writer and veteran political commentator.

"We don't really need American help, other than investment... That's where they will be dropping the big hints."

Clinton will also hold talks on a Northern Ireland economy reeling after house prices fell by over 50 percent since 2007. The troubles led to decades of under-investment and the province remains heavily dependent on a grant from London.

Financial services group Citigroup in 2010 announced the creation of 500 jobs in Northern Ireland weeks after Clinton held an investment conference for the province in Washington, but U.S. investment remains a tiny fraction of that in the Republic of Ireland.

(Writing by Conor Humphries; Additional reporting by David Brunnstrom; Editing by Tom Pfeiffer)