By Amanda Ferguson and Clodagh Kilcoyne

BELFAST (Reuters) - Irish nationalists in Belfast toasted Sinn Fein's historic election victory on Sunday while pro-British neighbours quietly fumed, but there was little sign the weekend's political earthquake was about to rock this once-troubled city.

In a victory that would have been unimaginable a few decades ago, the former political wing of the Irish Republican Army (IRA) on Saturday became the first Irish nationalist party to take top spot in elections to the British-run region's parliament.

The win gives Sinn Fein the right to nominate its leader Michelle O'Neill as the region's first Catholic First Minister - and more power to pursue the party's ultimate objective of uniting Northern Ireland with the Republic of Ireland to the south.

But few of the people enjoying a sunny Sunday on the city's staunchly pro-British Newtownards Road seemed overly concerned.

Obviously we don't want a united Ireland and Sinn Fein is going to push for a border poll but I'd say bring it on, we've nothing to be afraid of, said John Keenan, who runs the Union Jack Souvenir Shop.

His confidence is due to opinion polls that have consistently shown a majority of voters in Northern Ireland favour remaining part of the United Kingdom.

The pro-British loyalist community, named for their allegiance to the United Kingdom, is worried by Sinn Fein's rise, Keenan said.

But it also knows that Sinn Fein cannot rule without the consent of the largest pro-British party, the Democratic Unionist Party, under the region's carefully crafted 1998 peace deal.

That brings the prospect of direct rule from London if no agreement can be reached, which Keenan said would make him and many others happy.

Walking with a friend nearby, Methodist Protestant Church minister Gary Mason said that though many loyalists - and more moderate pro-British unionists - are probably in shock at Sinn Fein's success, many others were not at all surprised, seeing it as the consequence of constant infighting among pro-British politicians.

Sinn Fein pushing for a unification referendum is nothing new, he said.

'DIE HAPPY'

Across the city, wearing a Gaelic football jersey sporting the green, white and orange tricolour of the Irish Republic, 80-year-old Belfast man Tommy Shaw said he was quite pleased by Sinn Fein's win. He said he would die happy if Irish unification was achieved.

But he too expressed doubts that a referendum on unification was closer as a result of Sinn Fein's win. Not particularly, he said as he enjoyed a drink with friends at a sports club named after a nationalist leader who fought for Irish independence.

While Sinn Fein activists and candidates held a party on Saturday, there were no big celebrations in the nationalist stronghold of the Falls Road, where Shaw's Gaelic football team plays.

That reflected the fact that many see the victory as a stepping stone and that the referendum required to leave the UK is at the discretion of the British government and likely years away.

The biggest consequence of last week's vote could instead be a doubling of the number of seats won by the cross-community Alliance Party as it attracted the support of both Irish nationalists and pro-British unionists disgruntled with their traditional parties.

I think that's been brilliant, they are showing that there is a middle ground there, Shaw said.

(Writing by Padraic Halpin and Conor Humphries; Editing by Daniel Wallis)