In a serious blow to the already-battered Social Democratic Party, Wataru Kubo, former deputy prime minister and finance minister, on Jan. 6 said he will leave the SDP, a Diet ally of the ruling Liberal Democratic Party.SDP officials said at least six other Upper House members also are quitting with Kubo, who said he may join the Democratic Party of Japan, and most of the others are also expected to follow suit.The SDP, once a longtime opposition force before recently allying with the LDP, has seen a substantial decline in its Diet strength since the fall. It is now the fifth-largest force in the Lower House.The defection by Kubo, a one-time party secretary general, marks another setback for the party leadership of Takako Doi. “I have decided to leave the SDP to seek a way to unite liberal forces that are currently scattered in several political parties,” Kubo told a hastily arranged news conference.Besides the 67-year-old Upper House member, at least six other SDP Upper House members have recently informed SDP Secretary General Shigeru Ito of their intention to leave the SDP. Ito said the party will hold an urgent meeting of its current top executives to discuss the matter, adding that the SDP will continue to ask the lawmakers to remain.Kubo, a member of the SDP for more than 35 years, said liberal forces should unite to counter the powerful LDP. He said the SDP cannot play that role. “If we allow things to remain as they are, the LDP will gain an unprecedentedly huge amount of power,” Kubo said, adding that the LDP has already started to push its will onto Diet matters, including the compilation of the fiscal 1997 budget.