A labor group in South Korea said today it will stage a four-day strike this week to demand a shorter workweek and to protest a possible takeover of an ailing South Korean carmaker by a foreign investor. The Korean Confederation of Trade Unions asked its half-a-million members to walk off their jobs from Wednesday to Saturday. The labor group, with members in the car and shipbuilding industries is demanding the workweek be cut from forty-four to forty hours. Major businesses are opposed to a shorter workweek.