P245 CEEFAX 245 Mon 4 Apr 18:11/08    WALL STREET    (Midday): Blue chip stocks fell more than 80 points in morning trading before recovering nearly half their losses. The Dow Jones industrial average was down 47.50 at 3,588.46 at midday on very hjavz volume of about 140 million shares. A 50-point drop in the first 10 minutes activated the automatic limit on computer trading, which slowed the market'u descent.  World indices 243 Dow Jones 242 Euro/East Dow Jones Exchanges World Ind