The average price at the pump for a gallon of diesel fuel dropped one penny this week, according to statistics released yesterday by the Dept. of Energy. According to the department's Energy Information Administration, the average price slipped to $1.529, which is 22.3 cents lower that it was at the start of the war in Iraq. Crude prices have dropped from a pre-war $40 a barrel because the war in Iraq did not cause damage to oil facilities in the Persian Gulf region. They dipped further as the U.S. announced oil from Iraq might soon hit the open market. However, oil prices have crept back up in the last two trading days because the Organization of Petroleum Exporting Countries is expected Thursday to trim output to prevent a price collapse. For the second straight week, the Central Atlantic region has the highest average price, $1.688. New England follows close behind at $1.685.