Shareholders of Pacific Gas Transmission approved a merger with Pacific Gas & Electric . . . Capital Cities/ABC said that it intends to buy back about 310,000 of its shares periodically beginning Jan. 27 and that an employee stock ownership plan intends to buy about 280,000 of the shares . . . AT&T said it and a number of other telecommunications firms signed agreements for construction of two underwater light-wave cable systems that will span the Pacific Ocean by mid-1989 . . . James River Corp. and Crown Zellerbach have agreed in principle to settle a class-action suit against them concerning Zellerbach's "poison pill" rights . . . Midcon and Occidental Petroleum said they have received requests from the Federal Trade Commission for additional information concerning Oxy's proposed acquisition of Midcon . . . Argo Petroleum and Berry Petroleum said they have approval from their boards to pursue negotiations regarding a proposed merger of the two firms.