Milwaukee County Employees Retirement System, Milwaukee, has narrowed to five finalists its search for a domestic midcap equity manager to run at least $40 million, said Jac Amerell, director. The search was undertaken this summer because the $1.5 billion system had concerns over the performance of incumbent Firstar. Firstar, which rebid, is a finalist; the other finalists were not identified. Mr. Amerell expects an announcement to be made in late January. Officials at Firstar did not respond by press time.