Asked if he could see Manila adopting a new parliamentary form of government and still hosting the annual summit, Romulo said it would not present a problem.
But any amendments to the Constitution that lead to a parliamentary system would still have to be approved by the people in a referendum, he added.
"That is speculative. But we have to consult the people who have the final say. What I’m saying is the ultimate judge is the people. Any changes in the Constitution will be submitted in a plebiscite."
The Philippines will take over the ASEAN chairmanship from Malaysia next year after junta-ruled Myanmar announced last month that it would give up its turn to head the regional grouping in order to focus instead on its political reconciliation efforts.
Myanmar came under strong international pressure, including from the United States, to give up its turn to head ASEAN because of its poor human rights record and its refusal to release democracy leader Aung San Suu Kyi.
The other members of ASEAN are Brunei, Cambodia, Indonesia, Laos, Singapore, Thailand and Vietnam.
In her State of the Nation address last month, President Arroyo had urged Congress to amend the Constitution and change the form of government from the US-style presidential system to a federal parliamentary system.
She said the shift would end the legislative gridlock inherent in the current system, inherited from the US colonial era, and speed up the passage of laws needed to revitalize the struggling economy.
However, the Senate may again block any new attempts to amend the Constitution — just as it did last year — because most senators disagree with Charter change proponents over when and how to carry out amendments.
The move to amend the Constitution was revived by former President Fidel Ramos, who suggested the proposal after Mrs. Arroyo’s political crisis erupted.
Ramos said the move would also give Mrs. Arroyo a "graceful exit" amid opposition-led calls for her resignation over allegations that she cheated in last year’s presidential election.
Mrs. Arroyo has admitted phoning an election official during the May 2004 vote count but denied rigging the outcome. She refuses to resign but has welcomed an impeachment challenge to clear her name.
Article 17 of the Constitution provides three methods for introducing amendments: by constituent assembly, constitutional convention or a people’s initiative.
In a constituent assembly, Congress would propose amendments while in a constitutional convention, delegates elected by Filipinos to the panel would introduce amendments.
In a people’s initiative, at least 12 percent of the electorate may propose changes through a petition. All proposed amendments are to be ratified by the people in a plebiscite.
Congress may sit as a constituent assembly if both its chambers each adopt a resolution for the purpose. Last year, the House of Representatives passed such a resolution but a similar measure did not make it through the Senate.
Past attempts to amend the Charter during the administrations of Ramos and Joseph Estrada were blocked by strong public opposition fueled by memories of the brutal Marcos dictatorship. Most Filipinos fear that Charter change proponents would seek to remove elective officials’ term limits.
Term limits were put in place when the Constitution was rewritten in 1986 to prevent a repeat of the Marcos dictatorship as well as prevent abuse of power.