A BITTER court fight among leaders of the Singapore Democratic Party (SDP) could end this week with the island republic's small opposition representation in Parliament reduced from four to three seats. But even if Chiam See Tong, chief founder and former leader of the SDP, wins his battle to retain his membership of the party and, by extension, his seat in Parliament, the angry recriminations in court are going to make any future co-operation between the parties in the case difficult, if not impossible. Either way, the dispute will have damaged the SDP and reduced the early prospect of the opposition camp launching a plausible challenge to the ruling People's Action Party (PAP), which has been in power for more than three decades and holds 77 parliamentary seats. Mr Chiam, who was first elected to Parliament for the SDP in 1984, is seeking to overturn a decision by the central executive committee to expel him from the party after he criticised members in a public address. Under Singapore's constitution a Member of Parliament may not retain his seat if he ceases to represent the political party under which he was elected. Some SDP members say that a win by Mr Chiam could lead eventually to the formation of a breakaway party. This further fracturing of the PAP's political opponents, who are distributed among two main parties - the SDP and the Workers' Party (WP) - would lessen the likelihood of the PAP facing a united opposition front in the medium term. Tentative moves towards an alliance of the SDP and WP last year were abandoned in the face of intractable personality differences between Mr Chiam and Joshua Jeyaretnam, WP secretary-general. The current SDP executive committee includes two former members of the WP, Wong Hong Toy and Low Young Nguan, who, Mr Chiam said, were prejudiced against him when the decision was taken to expel him from the party. He described the executive committee hearing as a ''kangaroo court''. But Mr Chiam reserved his strongest criticism for the SDP chairman and a fellow SDP Member of Parliament, Ling How Doong. Mr Ling has been chairman since 1987. ''He just intended to thumb me down, to exercise his authority, to humiliate me and to get the matter over as quickly as possible,'' Mr Chiam said. Mr Ling responded by saying the executive committee had done no more than follow the party constitution. He characterised Mr Chiam as ''evasive'', ''defiant'' and ''arrogant''. ''He had that sort of attitude: 'I'm a great man, who are you to sit in judgment over me?' '' Mr Ling said. The court case has not only revealed disarray within the leadership but uncovered a link between the structures of the SDP and the PAP. The court was told that the party's constitution vested considerable power in the executive committee. When Justice Warren Khoo suggested this was ''a bit strange'', he was told it was ''modelled on a well-known political party''. Party members confirmedthat was the PAP.