Irish voters face a month of intensive campaigning and a crucial vote on the enlargement of Europe after Bertie Ahern's government yesterday announced that its long-awaited second referendum will be held on October 19.  Mr Ahern's decision on the date for a second Irish vote on the EU's Nice treaty injected new drama into plans to expand the union by up to 10 new members.  Ireland is the only EU member constitutionally required to ratify the treaty, a complex and bitterly contested document which reformed EU voting mechanisms and institutional arrangements to enable it to function in the future, but last year Irish voters voted against by 54% on a 32% turnout. "I think it would be a disaster for this country not to ratify this," warned Mr Ahern.  "The vote on the second referendum on the Nice treaty will be a defining moment for Ireland and for Europe," said Pat Cox, the Irish president of the European parliament.  "There is a lot at stake. A second rejection of the treaty would plunge the European Union's main strategic agenda, that of enlargement, into a pe riod of uncertainty and potential crisis."  The EU summit in Copenhagen in December is expected to name the successful candidates for EU entry. The treaty has to be ratified by then.  Last year's rejection of the treaty was a devastating blow for the EU and starkly underlined concerns about the sense of "disconnect" between ordinary citizens and remote and distant institutions.  Opponents, including Sinn Fein, mobilised support by claiming Ireland would lose its military neutrality and forfeit control of economic growth and immigration in an enlarged Europe.  It was all the more alarming since Ireland had benefited hugely from its membership since joining the then EEC along with Britain in 1973 and was always considered one of the most Europhile countries.  EU governments and candidate countries stretching from Estonia to Malta are fervently hoping that this campaign will be more effective than the last.  "This, in terms of a campaign, will be a real campaign," Mr Ahern promised. "We're spending a large amount of money which we don't have, but we feel obliged to do that."  The background is not promising. The referendum commission, a government- appointed body designed to encourage people to vote, said on Wednesday that it had polled 300 people on the treaty - and found that only 16% understood it. Only 24% of young voters planned to participate.  Another recent poll showed 44% of voters were undecided.  The poor prospects may serve as a lesson for a future euro referendum in Britain.  Last year, the Irish opponents' most memorable slogan was: "If you don't know, vote no." This time round, "no" campaigners are expected to argue the very fact that the referendum is happening again is evidence of a lack of respect for democracy, suggesting the Irish will be forced to vote until a majority says "yes".  In Brussels, EU officials insist publicly there is no politically acceptable alternative to ratification by the Irish, but privately some admit that complex legal moves could solve the problem.  The treaty, negotiated on the French Riviera in December 2000, reduces national veto powers but preserves the dominance of big countries such as Britain, France and Germany.  All the main Irish political parties and business groups support a yes vote. But that was also the case when Denmark rejected the euro two years ago. Classification Language: ENGLISH Subject: EUROPEAN UNION (92%); VOTERS & VOTING (91%); TREATIES & AGREEMENTS (90%); REFERENDUMS (89%); EUROPEAN UNION ACCESSION (78%); EUROPEAN UNION INSTITUTIONS (78%); APPOINTMENTS (78%); INTERNATIONAL ECONOMIC ORGANIZATIONS (76%); LEGISLATIVE BODIES (73%); POLLS & SURVEYS (62%); IMMIGRATION (50%) Company: EUROPEAN PARLIAMENT (55%); EUROPEAN UNION (55%); EUROPEAN UNION (55%); EUROPEAN PARLIAMENT (55%) Organization: EUROPEAN PARLIAMENT (55%); EUROPEAN UNION (55%); EUROPEAN UNION (55%); EUROPEAN PARLIAMENT (55%); EUROPEAN PARLIAMENT (55%); EUROPEAN UNION (55%); EUROPEAN UNION (55%); EUROPEAN PARLIAMENT (55%) Person: BERTIE AHERN (79%) Geographic: EUROPEAN UNION MEMBER STATES (95%); IRELAND (94%); EUROPE (94%); ESTONIA (79%); UNITED KINGDOM (79%); MALTA (78%)