Pacific Mutual OKs Merger for Giant Brokerage : Investments: Five subsidiaries of the Newport Beach insurer and a Connecticut group will manage $70 billion.

Pacific Mutual Life Insurance Co. and Thomson Advisory Group L.P. said Tuesday that they have signed a final agreement to merge Thomson and five of Pacific Mutual’s investment management subsidiaries into one of the world’s largest investment companies.

The combined businesses, to be named Pimco Advisors L.P., will manage assets of nearly $70 billion. The companies said they expect a Sept. 30 completion of the merger, which was originally announced in March.

A new partnership between Newport Beach-based Pacific Mutual and its Pacific Investment Management Co. subsidiary is scheduled to become general partner of Pimco Advisors after obtaining a controlling interest in the present general partner, Thomson Advisory Group Inc. in Stamford, Conn., for $125 million.

William D. Cvengros, now vice chairman of Pacific Mutual, would leave that post to become the chief executive officer of Pimco Advisors.

Thomson officials said Tuesday that as part of the deal they would issue 300,000 new shares to Thomson investors, or unit holders, as a special 3% dividend. The dividend will be worth about $5 million a year through 1997 to the company’s public investors because their cash dividend payments will rise to $3.75 per unit each year from $2.60 paid in 1993.

Pacific Mutual and its investment managers will control about 81% of the combined business, which would have a market value of about $1.24 billion based on the price of Thomson’s existing units, which closed up $2 on the New York stock exchange Tuesday at $38.785. Pacific Mutual Life is not publicly traded.

The merger will give Pacific Mutual’s investment divisions a network of brokers to sell investments to the public. Those divisions have typically handled investments for large, outside investors, such as pension funds and corporations. The combination of the Pacific Mutual and Thomson divisions will create the nation’s sixth-largest financial management company.

The consolidation will place three Thomson Advisory Group L.P. businesses--Columbus Circle Investors, Thomson Fund Group and Thomson Investor Services--with the Pacific Mutual investment management businesses in the new Pimco Advisors L.P.

The Pacific Mutual subsidiaries involved are Pacific Investment Management Co., Newport Beach; Cadence Capital Management Corp., Boston; NFJ Investment Group, Dallas; Parametric Portfolio Associates, Seattle; and Blairlogie Capital Management Ltd., Edinburgh, Scotland.