By Andras Gergely

DUBLIN (Reuters) - German Chancellor Angela Merkel called on Irish voters on Monday to back the European Union reform treaty, as a new poll showed a majority of Irish were undecided about how they would vote in the June 12 referendum.

Ireland is the only EU country planning a referendum on the treaty and a "No" vote from one of the bloc's smallest states could topple the project designed to end years of wrangling over reform of Europe's institutions.

The treaty gives the European Union a long-term president, a stronger foreign policy chief, a streamlined decision-making system and more say for national and European parliaments.

Merkel's visit came as a Red C poll in The Irish Sun newspaper showed 60 percent of voters were undecided on whether to back the successor to the EU's failed constitution. Just 28 percent planned to support it and 12 percent were opposed.

Of 1,001 people surveyed, 65 percent said they had very little or no understanding of the treaty, 28 percent had some understanding and 6 percent professed to have a full grasp.

"It is not always easy to understand how Europe works," Merkel said during a visit to Dublin.

In a speech to Irish lawmakers, she drew on her experience growing up in communist East Germany to extol the virtues of the European Union.

"Looking back on my own life, unification and the creation of the European Union is the best thing that has happened in Europe and its long history," Merkel said.

"To my mind, the Lisbon (reform) treaty offers the best preparation for Europe's future."

IRISH NEUTRALITY

Irish voters are seen as some of the most pro-European in the EU -- 89 percent surveyed in Monday's poll said membership had been good for Ireland -- but in 2001 they rejected the Nice Treaty designed to enable EU enlargement.

That "No" vote forced the government to hold a second referendum that was widely criticised as undemocratic. Ministers have accepted such a re-run is not an option this time round.

Most Irish politicians favour the pact but outgoing Prime Minister Bertie Ahern has acknowledged the government faces an uphill battle to convince people of the treaty's merits due to its lack of radical reforms.

Opponents see Merkel's visit as part of a pro-treaty drive by EU heavyweights to sway voters. European Commission President Jose Manual Barroso is to visit Dublin later this week.

"Over the coming weeks I am sure that many EU leaders will be scrambling to our shores to lobby for a yes vote in the referendum," said Mary Lou McDonald, a European lawmaker and member of the Irish nationalist Sinn Fein party.

Sinn Fein is the only political party represented in Ireland's Dail (lower house of parliament) opposed to the treaty. It has four seats in the 166-seat chamber.

Responding to Merkel's speech, McDonald said the treaty rehashed a constitution rejected by French and Dutch voters in 2005 and would weaken Ireland's influence.

"Ireland is traditionally a neutral state and that neutrality is underpinned by a capacity to have an independent foreign policy position," McDonald told the audience, adding that the treaty "undermines that yet again".

Merkel denied it creates a European super-state.

"The Irish prime minister can at any time say we're not for this and it won't be common foreign policy," she said.

(Writing by Paul Hoskins; Editing by Mary Gabriel)