EU President Herman Van Rompuy argued Friday that the 17-state eurozone could have a central \'Treasury\' with a shared budget and raise funds on commercial bond markets.   In a report proposing closer economic integration, drawn up for a summit of European Union leaders next week, Van Rompuy spelt out the rationale behind plans to take the eurozone potentially beyond a purely inter-governmental structure.   Van Rompuy said the hypothetical central budget for the eurozone -- home to some 340 million people as distinct from the full, 27-state EU, including non-euro economies like Britain and Poland -- would need fine-tuning between now and a December summit.   Depending on how these ideas proceed, leaders may have to embark on a fresh, controversial round of EU treaty changes, with the risk that London, especially, might call a referendum to redefine its relationship with the Brussels-based bloc.   \"One of the functions of such a new fiscal capacity could be to facilitate adjustments to country-specific shocks by providing for some degree of absorption at the central level,\" Van Rompuy wrote.   Another key aim would be to \"facilitate structural reforms that improve competitiveness and potential [economic] growth.\"   The eurozone this week signed into life its new financial firewall, the European Stability Mechanism, a rescue fund ultimately worth 700 billion euros ($910 billion), which Van Rompuy said was for emergencies.   Long-term, the former Belgian premier also opened a door towards pooled eurozone government issuance of bonds, or borrowings.   He said a key aspect of the centralised eurozone budget would eventually be the capacity to borrow against it.   Overall, the idea is that national governments would strike deals with central eurozone supervisors -- legal commitments like those enacted in Greece and elsewhere that would theoretically make the eurozone a more homogenous territory.   These could involve loss of sovereignty.   According to one EU official, it\'s about \"convergence between national economic policies.\"   In the view of Brussels strategists, such a plan could help the eurozone to \"sustain assymetric shocks,\" meaning dangers posed by less competitive parts than Germany.   A big question will be to what extent Berlin might compromise on over-competitiveness by comparison with Greece or Spain, for example.   A debate going into the summit is whether this system -- albeit on the drawing-board -- would be imposed all round, or only on states that have consistently failed to balance books.