Ireland faces an uphill battle to get the Lisbon Treaty ratified in a referendum next month, Foreign Minister Micheal Martin admitted yesterday, threatening once again EU ambitions for greater global influence.

Europe's plans for an overhaul of its foreign policymaking and internal decision-making rest on Irish voters, who account for less than one per cent of the 27-nation bloc's population, and who rejected the charter in a referendum last year.

An opinion poll on Thursday showed that support for the treaty has fallen with just four weeks to go till polling on a second vote on October 2.

"I was never under any illusion but that it would be difficult to secure this but I do think we can do it," Mr Martin told national radio RTE.

"There is a very significant challenge ahead, it's going to be a very tight campaign and it will demand all of the resources, conviction, politics and passion of all of those on the Yes side."

The "Yes" camp is still ahead in opinion polls but there has been an increase in the number of undecided voters, reflecting how important campaigning will be over the next four weeks.

Analysts have warned, however, that the government's deep unpopularity could trigger a significant protest vote and lingering confusion over the treaty and the workings of the EU could work against a resounding "Yes".

The treaty has to be ratified by all 27 member states before it can take effect and Eurosceptic presidents in Poland and the Czech Republic have said they will wait for the Irish vote before signing it into law in their countries.

Last year's poll was lost due to voter confusion, a lacklustre official campaign and a fired-up opposition which captialised on both, putting the government on the back-foot with emotive arguments about abortion, neutrality and taxation.

This time around, Dublin has won concessions from Brussels on key policy areas, including the right to retain an EU commissioner, and has vowed not to repeat the mistakes of the last campaign.