FED'S JOHNSON SAYS LOUVRE ACCORD STILL VITAL Federal Reserve Board Vice Chairman Manuel Johnson said the Louvre Accord is still healthy, but said the United States and West Germany must work out differences over their respective roles in fulfilling the accord. "The Louvre Accord has worked very well in terms of stabilizing exchange rates," he said in response to a question during an American Stock Exchange conference here. He said exchange rates have been stable so far in 1987 as a result of the accord.