For years, Japanese businessmen have been flying to San Francisco Seattle and Los Angeles to shop at Brooks Brothers, and now Brooks Brothers is going to Japan.

Plans to open eight Brooks Brothers stores in Japan in the next five years-starting in Tokyo next fall-were announced yesterday by the company, part of Garfinckel, Brooks Brothers, Miller & Rhoades of Washington.

Daido Worsted Mills, a Japanese clothing and textile manufacturer and retailer, will be Brooks' partner in the venture, the company said.

But the stores will be strictly Brooks Brothers-natural shoulders, button-down collars, pin stripes and all. They'll sell suits, ties and shirts made by Brooks Brothers and other apparel items manufactured to the company's specifications, said Frank T. Reilly, president of the 19-store chain.

Unlike some American retailers who franchise their name to foreign partners but sell foreign-made merchandise in the stores, Brooks Brothers' Japanese stores will sell the same goods ast he firm's U.S. units, he said.

Reilly will be chairman of the board of the Japanese venture, and Daido will appoint the firm's president.Brooks will supervise manufacturing and selection of merchandise; Daido will run the stores.

The Japanese venture will be the first overseas operation for Garcinckel, which has a corporate goal of increasing sales and profits by 20 percent per year through acquisitions and expansion.