Electoral gains by opponents of the Nice European Union enlargement treaty have complicated the Irish government`s task of convincing voters who rejected the treaty last year to change their minds in a second referendum.

The hardline nationalist Sinn Fein, which spearheaded the anti-treaty campaign last year, advanced to five seats in last Friday`s election while the Green Party won six. The most pro-Europe party, the opposition Fine Gael, suffered a meltdown.

"I think whatever government comes into power is going to get its knuckles rapped again by the people if they attempt to re-run the Nice Treaty with only cosmetic changes," Trevor Sargent, the Green Party leader, said on state-run RTE radio.

Ireland threw the EU`s expansion plans into turmoil last June when a referendum rejected the treaty, aimed at reshaping the bloc`s institutions to cope with the admission of a dozen new members.

An opinion poll just before the Irish election showed declining pro-treaty sentiment and gains for opponents, with about a third in favour, a third against and a third undecided.

Prime Minister Bertie Ahern, who swept into office for a second term with the biggest mandate in years, has said he will hold another referendum on the treaty, probably in October.

But Ireland`s most popular prime minister in decades has his work cut out for him.

Daniel Keohane, a researcher with the Centre for European Reform in London, had no doubt of the vote`s importance.

"It doesn`t just affect Ireland, it affects the rest of the EU," he said. "And it will be a very difficult situation on the EU level with the applicant states and for Ireland as well if Ireland votes `no` a second time."

The Nice Treaty has been ratified by the parliaments of the other 14 EU member states.

Ireland, which alone of the current EU member states must ratify such treaties by referendum, rejected the treaty last June by a vote of 54 to 46 per cent. If it is not approved by the end of the year, the treaty will expire.

The reasons for Ireland`s rejection of the treaty were complex. Some critics said it would infringe on the country`s tradition of military neutrality. Both Sinn Fein and the Greens take that view.

Others argued that Ireland would lose out through the EU reforms, particularly by the loss of its guaranteed seat on the executive European Commission.

But many analysts on both sides of the argument think the treaty really lost because of a lacklustre campaign by its champions, including Ahern`s centre-right Fianna Fail party.

It also failed because Ireland, once considered "the best pupil in the EU class", is simply unsure whether it wants to go along with a stronger central administration in Brussels.

"There is a consensus in the middle ground in favour of European integration, the main parties of the centre are pushing for more integration all the time," said Anthony Coughlan, a lecturer in social policy at Trinity College and a supporter of the "no" vote in June.

"But the Irish electorate is certainly getting more eurosceptic all the time, and with good reason," he said.

Clodagh Harris, lecturer in government at University College, Cork, said the new parliament`s composition "certainly doesn`t make Bertie Ahern`s task of ratifying the Nice Treaty any easier.

"However that can also be seen perhaps as a positive if you consider that one of the criticisms of the first Nice campaign was that there was a lack of debate and a lack of information on the matter," she said.

She said the bigger presence in parliament for Sinn Fein and the Green Party could force a more open debate, while other analysts said it would put the parties on the spot to explain what their alternative is to the Nice Treaty and enlargement.

Keohane also said the pro-treaty forces did a bad job of salesmanship last time around.

"You know Ireland has done well, people get a bit conservative, they don`t want to rock the boat," he said.

"What they didn`t manage to sell was that we actually got a very good deal at Nice. We`re going to gain politically and it`s not just the point generally that enlargement is good for the EU, it`s very good for Ireland."