TWO weeks behind the deadline it set itself, Japan's new ruling coalition has finally reached consensus on a political reform plan that will radically change Japan's democratic structure. However, it appears to have backtracked on one key issue - political donations from Japanese business corporations. A crucial element behind the delay in reaching a compromise was the need to try to secure the support of the Socialists for the proposed reforms, thereby preventing them from breaking up, and even bringing the coalition down. In the end, the ideas favoured by the Socialists, led by Political Reform Minister Sadao Yamahana, the Japan New Party (JNP) led by Prime Minister Morihiro Hosokawa, and the New Forerunner Party led by Chief Cabinet Secretary Masayoshi Takemura generally carried the day. First and foremost, under the agreed plan, the next House of Representatives will consist of 500 members, half elected in single-seat constituencies, and the other half elected through proportional representation. The current Lower House consists of 511 members chosen in 129 constituencies which return between three and six members each. Second, the coalition has agreed that each Japanese voter will have two votes, one for the candidate of their choice in their home constituency, and one for the political party of their choice with proportional representation. A major cause for the delay in reaching consensus on the plan was the opposition of the Japan Renewal Party led by Deputy Prime Minister Tsutomu Hata, and the Clean Government Party, which both urged 300 single member constituencies and only 200 seats through proportional representation, and wanted single votes. The secretary-general of the Japan Renewal Party, and the widely acknowledged political architect of the coalition Government, Ichiro Ozawa, also argued strongly in favour of the single vote, under which a vote for one candidate in a constituency would be also counted as a vote for that candidate's political party under proportional representation. Mr Ozawa evidently took this line believing such a system would hasten the integration of the coalition into a single group or party, which would speed up the development of a two-party system. Despite the fact that the 250-250 formula was pushed by Mr Yamahana, many members of the Socialists are opposed to it. Further, Mr Yamahana, in order to try to keep his party together, has had to resign as Socialist leader, taking responsibility for its severe loss of seats in the last election, and will be seeking re-election to that post at a special convention next month. The Socialists are currently the largest party in the coalition with 76 seats. If the left-wing of the Socialists broke away, Mr Hosokawa's Government might lose its narrow majority. But on one crucial issue, corporate donations to political parties, neither the Socialists nor the Prime Minister have had their way. Mr Hosokawa in his policy speech in the Diet last Monday spoke of corporate contributions being at the heart of corruption scandals, and promised to ''move to outlaw all such contributions and to replace them with neutral untainted public funding''. Now it appears that the only corporate contributions which will be outlawed are those made to individual politicians. Mr Ozawa and the Japan Renewal Party insisted that contributions to political parties be retained, though under what conditions is not yet clear.