Inflation at the wholesale level moderated in March when the producer price index increased 0.4 percent, down from 1 percent hikes in February and January, the government said Friday. Slower increases in prices for food and energy accounted for the more modest rise in wholesale prices last month, which amounted to 5.5 percent on an annual basis. Still, for the first quarter of 1989, wholesale inflation jumped at an annual rate of 10.2 percent, the largest hike for any quarter since a 13.2 percent rise in the first three months of 1981, the government said.