NEW YORK — Act III Theatres Inc., in an aggressive expansionary mode, increased net profit 13% to $4.1 million in 1996 on 14% higher revenue of $223 million, it revealed in an SEC filing Thursday.But Act III’s spending on theater building increased dramatically during the year and forced the exhibitor to increase its credit line. Act III had opened four theaters with 39 screens in 1995 and acquired 27 screens, but last year it opened six theaters with 70 screens, taking its total number of screens to 673. The company said in the SEC filing that capital expenditures on theater openings and acquisitions jumped from $30 million to $68 million, which meant Act III did not have enough cash from operations to finance the building and had to amend its credit line to get an extra $25 million . In mid-February the credit line was increased again by $95 million to a total of $250 million, the filing said. Act III is 82% owned by Norman Lear and most of the rest of the stock is owned by two institutional investors: Electra Investment Trust Plc and St. Paul Fire and Marine Insurance Co.