The elected president's power to block key public service appointments is more important and should get greater emphasis than the custodial role over the reserves, rights group Maruah said.
This is because the president is in the position to safeguard the integrity and incorruptibility of the entire public service, its representatives Braema Mathi, 58, and Ngiam Shih Tung, 49, said yesterday.
Under the Constitution, the president can veto the appointment or removal of key public service office- holders such as the auditor-general and the chief of defence force.
Mr Ngiam cited the example of Malaysia, where the attorney-general was removed from office last year when he was investigating possible corruption at the highest level of the government there.
"We certainly do not want to see such a situation in Singapore," he said at the third session of public hearings by the Constitutional Commission that is reviewing the elected presidency.
Ms Mathi, who is Maruah's president, said the elected president's function as a second key to protect the country's reserves has come across as the office's main responsibility.
But in its written submission, Maruah described this custodial role as a "red herring" and said the president's power over financial matters is extremely limited.
Mr Ngiam said it is undemocratic for the president to block Supply Bills, which determine the Government's Budget, as these are passed by Parliament - a body that reflects the will of the people.
But Chief Justice Sundaresh Menon, who chairs the commission, questioned this notion and noted that the president is also elected and so has a mandate to exercise his custodial powers.
"In fact, some have suggested the president has a unique, almost national mandate because he goes through a national election."
Mr Ngiam said his concern was also that candidates are picked from a small pool of people who qualify based on strict eligibility criteria. The review of the eligibility criteria would shrink this pool and further limit the choices for Singaporeans.
This led the Chief Justice to say the intention of the review is not to reduce the number of people who can qualify to run for president.
Instead, it is to ensure the president has the necessary expertise to deal with the different functions of the office, he said.