The 15-nation EU will grow to 25 members once Cyprus, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia, and Slovenia join. The bloc is expected to further expand to 27 countries in 2007, when Bulgaria and Romania are likely to be admitted.
Analyst Joan Hoey, of the London-based Economist Intelligence Unit, told RFE/RL that the EU's executive body, the European Commission, is likely to show even more strictness toward future candidates.
"Although the [European] Commission is saying that negotiations are going to be on the same basis, obviously the whole climate has changed and is about to change [further] after May 2004. There is this enlargement fatigue. Support for enlargement is falling. There's a political backlash that's gathered momentum in some countries. There is growing skepticism about the implementation of the acquis in the eight East European countries that are joining in May, and there's a nervousness about the costs of enlargement," Hoey said.
In a sign that it means business when it comes to enlargement, the EU sent a strong warning to laggard candidate Romania last month, saying it risks missing the 2007 target unless it takes rapid and decisive measures to implement judicial reform, get rid of endemic corruption, and stop pressure on the free media.
A European Parliament report on Romania stopped short of recommending the suspension of accession talks, but issued a tough wake-up call for Bucharest to pursue a complete "reorientation" in the country's strategy for joining the EU.
Bucharest's slow progress toward fulfilling the admission criteria has raised the question of whether prospective candidates could be taken in before they are completely ready.
Analysts point to the example of Greece, which became a successful EU member despite its apparent unpreparedness when it was admitted in 1981, only years after having experienced a military dictatorship.
But analyst Kirsty Hughes, of the Brussels-based Center for European Policy Studies (CEPS) says accepting unprepared members after this year's huge expansion could undermine the EU.
"Obviously, if countries are brought in when they're not fully ready, especially when we're facing such a big enlargement [with] so many new member states, then the more member states you have who aren't acting as they should, who aren't implementing laws as they should, who aren't following the rules as they are, who aren't true democracies, then that is potentially going to undermine the EU unless the EU applies the sanctions it has, that it can use against member states. But the more member states that are breaking the rules, the more difficult it is to apply serious sanctions against them," Hughes said.
Countries in the western Balkans, such as Croatia, Bosnia, Macedonia, Albania or Serbia and Montenegro, have also expressed interest in European integration, with Croatia best positioned to be accepted as a candidate.
Farther east, Moldova, Ukraine, and, more recently, Georgia have made no secret of their European aspirations.
Experts say the way the EU treats Romania's candidacy could become a case study for other, more distant, EU hopefuls.
Political analyst Tom Gallagher, of the University of Bradford in Britain, told RFE/RL that he believes the EU would be taking a risk by accepting Romania before it is fully ready for membership.
"If the accession process regarding Romania went wrong, and Romania turned out to be a huge headache for the EU after it became a full member, I think the motivation and commitment for expanding to the rest of the Balkans would diminish, and people would just shrink from the bigger task of integrating countries in the Caucasus and farther east," Gallagher said.
Hughes of CEPS says any future expansion beyond Bulgaria and Romania will largely depend on how the EU shapes itself over the next several years.
"I think what we have to look very much for [is] what happens in the next three, four, or five years -- how much the EU changes, how difficult it finds it to operate at 25 [members], whether it becomes a rather looser, for instance, sort of organization. All those questions are very much unknown and that, therefore, impacts on what you could say about future candidacies from the western Balkans or even from countries like Georgia or Ukraine. I think it's perfectly feasible to imagine that in the next five to 10 years, a country like Croatia may join the EU, but whether countries like Bosnia or Albania are going to be ready -- even in the medium run -- is quite unclear," Hughes said.
But Hughes also warns that EU membership may remain a bridge too far for many eastern countries. She points to the fact that the current political trend within the EU favors partnership agreements with future neighbors over promises of full-fledged membership.
"When one looks farther east, the EU itself has a political decision to make about whether it is at any point going to say, 'We have borders. We have a point when we stop expanding. We have a point when we try and make good friends and associates with our neighbors rather than members.' And I think what the EU has clearly been trying to do in the last year or so is to say to countries like Ukraine and Moldova, 'You are really not on the agenda of potential candidates for 20 years or more, so please don't even try and talk about it. Let's talk about building good relations.' That may not be what Georgia [for example] wants to hear, but that, for the moment, is current political reality," Hughes said.