++++ AGRICULTURE - COMMON ORGANIZATION OF THE MARKETS - BEEF AND VEAL - PURCHASE OF MEAT FROM INTERVENTION AT A PRICE FIXED IN ECUS - CHANGE IN THE REPRESENTATIVE RATES AFTER THE CONCLUSION OF THE PURCHASE CONTRACT - FAILURE OF THE PURCHASER TO CARRY OUT THE CONTRACT - FORFEITURE OF SECURITY - PRINCIPLE OF PROPORTIONALITY - INFRINGEMENT - NONE ( COMMISSION REGULATION NO 2173/79, ART . 16*(2 )*)