SINGAPORE: Deputy Prime Minister Ong Teng Cheong, 56, appears set to become Singapore's next president. Mr Ong agreed yesterday to be nominated as a candidate for the post by the National Trades Union Congress (NTUC), which he heads as secretary-general. Singapore's constitution was amended in 1991 to facilitate the election of a president. The first poll is due before the end of this month, when the term of the incumbent expires. However, with no challenger in sight, Mr Ong is expected to be the sole nominee and next president. The constitutional amendment stipulates that, if there is only one candidate on nomination day - which falls five days after an election writ has been issued - the returning officer will declare that person duly elected for a six-year term. The current office-holder, President Wee Kim Wee, 77, has indicated he will retire when he completes his second four-year term on September 1. When the constitution was amended, many political observers thought that former prime minister Lee Kuan Yew, now Senior Minister, would become president. But he has repeatedly denied this. Both Mr Ong and the other Deputy Prime Minister, Lee Hsien Loong, the elder son of Senior Minister Lee, were diagnosed as having cancer last year. But Mr Ong's illness was less serious than his colleague's and he has not had to undergo prolonged treatment. Mr Lee, on the other hand, underwent chemotherapy treatment and has yet to assume a full workload. Political observers had speculated that Mr Ong might be a candidate for the presidency when a new cabinet minister, Lim Boon Heng, was appointed last week. Mr Lim, a former official of the NTUC, has the qualifications to take over Mr Ong's job as secretary-general. A statement by the NTUC said Mr Ong was the ''most appropriate person for this very important post''.