CROPS DEVASTATED
Four-day freeze destroys more than third of California's annual citrus crop, inflicting half-billion dollars in damage and raising prospect of tripled orange prices in supermarkets by next week; farmers frantically run wind and irrigation machines in effort to keep treees warm, but lemon crop is near total loss and half of state's orange crop is lost; citrus industry accounts for over $1 billion of state's $27 billion agricultural output; cold is threatening other crops as well; photo; map (M)