DUBLIN (Reuters) - Irish voters rejected a treaty on Friday to overhaul the European Union's unwieldy institutions, putting the entire bloc's reform plan in peril and humiliating Ireland's political leaders.
The pact, known as the Lisbon treaty, failed by a margin of 53.4 to 46.6 percent in the only EU country to put it to a popular vote.
"No" vote supporters cheered loudly for several minutes, interrupting an official as he read out the results.
Prime Minister Brian Cowen called the vote "a source of disappointment to my colleagues in government and to me."
"In a democracy, the will of the people as expressed at the ballot box is sovereign. The government accepts and respects the verdict of the Irish people."
The treaty was an effort to resurrect EU reforms that were torpedoed by French and Dutch voters in 2005.
This time all countries but Ireland avoided a referendum. The "No" vote means a country with fewer than 1 percent of the EU's 490 million population could doom a treaty painstakingly negotiated by all 27 member states.
European Commission President Jose Manuel Barroso urged the other 26 members to press on and ratify the treaty. Fourteen have already done so and another four are close.
The treaty envisages a long-term president of the European Council of EU leaders, a stronger foreign policy chief and a mutual defence pact. It was due to take effect on January 1, but cannot come into force if a single member fails to ratify it.
Ireland ranks in surveys as one of the EU's most pro-European states. But the treaty's opponents persuaded voters that the pact would reduce the influence of small countries and undermine Ireland's jealously guarded historic neutrality.
Turnout was a healthy 53 percent, eliminating suggestions that voter apathy was to blame for the defeat of a measure supported by all three of Ireland's major political parties as well as farmers' groups, businessmen and many labour unions.
Electoral returns showed opposition to the treaty concentrated in working class areas where many people are suspicious of Brussels and of their country's political elite.
Ireland is one of the EU's great success stories -- once one of the poorest countries in western Europe, it is now one of the world's richest. But the economy has started to stall and many voters are uneasy with massive immigration and rapid change.
The euro fell to its lowest level in over a month against the dollar after the first reports suggesting a "No" victory.
EU leaders meeting in Brussels next week will have awkward questions for Cowen, making his European summit debut after taking over as prime minister last month.
"The result does bring about considerable uncertainty and a difficult situation. There is no quick fix," Cowen said. "We need to pause to observe what has happened and why, and to consult widely at home and with our European partners."
Brian Lenihan, the finance minister, said Ireland would have a hard time persuading other states to renegotiate the pact.
"We've already had seven years of negotiation and renegotiation," he said. "It's very difficult, having gone through plan A and plan B, to see where plan C lies."
Germany, France and Britain all said they would continue their efforts to ratify the treaty.
"We are sticking with our goal for it to come into force. The ratification process must continue," German Foreign Minister Frank-Walter Steinmeier said.
Other European leaders expressed hope that Ireland would still find a way to sign up to the pact.
"Ireland will for sure find a way to ratify this treaty," Polish Prime Minister Donald Tusk told reporters.
But Mary Lou McDonald, a member of the EU parliament from Ireland's nationalist Sinn Fein party, which helped lead the "No" campaign, said it would be impossible for Irish leaders to wriggle out of the referendum result.
"This is a moment of democratic truth here. Do you listen to the people or don't you?"
The treaty's failure, especially with robust turnout, was a surprise. On polling day bookmakers were still taking bets giving it overwhelming odds to pass.
It wasn't the first time Irish voters have shocked the EU. They almost wrecked the bloc's plans for eastward expansion in 2001 by rejecting the Nice treaty, but the government staged a second referendum in which that pact passed. The government has said it is not considering a re-run this time around.
(Writing by Peter Graff; Editing by Caroline Drees)
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