The European Union's chief on Monday called for a halt to further expansion of the bloc after Romania and Bulgaria join, saying the EU had to resolve the stalemate over its proposed constitution before it could accept new members.

European Commission President Jose Manuel Barroso said the 25-nation bloc was limited in its capacity to absorb more members without new rules to make an expanded EU work more effectively. He said the draft constitution answered those problems and needed to be salvaged.

Dutch and French voters rejected the EU charter last year and leaders from the bloc decided in June to postpone any decision on its future until 2007.

"It would not be wise to proceed with any further enlargement before we have dealt with the constitutional issue," Barroso told reporters after talks with French Prime Minister Dominique de Villepin. "It would be unwise to bring in other member states apart from Romania and Bulgaria."

Barroso's comments came a day before the release of an important progress report on whether Romania and Bulgaria could join the EU next year. While the report was expected to recommend that those two countries be allowed to join, Barroso's comments cast doubt over the membership bids of Croatia and Turkey.

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His remarks also reflected concerns about the union's ability to make decisions after Romania and Bulgaria join the 25 EU governments at the table. Key political decisions already are being taken after marathon negotiations.

The proposed EU constitution revamps the way its main institutions, the Commission and the council of EU governments, make decisions. It also does away with some veto rights to speed up decisions.

The European Commission was expected on Tuesday to lay out tough penalties for Romania and Bulgaria if they do not complete required reforms after they join, according to a draft copy seen by The Associated Press.

The report says the EU will propose close monitoring of food safety issues, EU subsidy programs and several justice and home affairs issues. All those reflect concerns that two Balkan countries, whose economies are a third the size of the EU average, have reputations for rampant corruption.

The commission had the option of recommending their entry be postponed for a year, but will not do so because a delay would do little to accelerate reforms, EU diplomats said. The two countries would get an automatic 2008 entry date and the Commission would have no bargaining power.

If they fail to meet EU standards, the bloc has reserved the right to start protective measures such as temporarily suspending some rights that come with membership. The EU also could temporarily freeze aid worth hundreds of millions of dollars.

Croatia and Turkey started entry talks last year, and Croatia was expected to finish its membership negotiations by 2009. Turkey's talks were expected to last decades.

"Of course I would like Croatia to join as quickly as possible, if it fulfills all the criteria," Barroso said. However, Croatia, Turkey and other Balkan nations that want to join fear the EU is imposing new obstacles.

Villepin agreed that the ability of the EU to take in new members had reached its limit.

"We have to make progress with our common rules before we can contemplate any further stages," Villepin said.