Florida is producing its biggest crop of oranges in a decade and is the beneficiary of the losses suffered by California's freeze, but the industry is uneasy about the future.

While growers are reaping a good harvest in a year that is so far frost-free, industry leaders know they have a major challenge ahead in selling all of the processed juice that will be squeezed from bumper crops foreseen in the coming years.Unless new markets are developed for the state's principal product, frozen concentrated orange juice, the bigger crops can mean much lower prices, and smaller profits for the grower, processor and so on up the line.

State and federal analysts forecast a 1990-91 orange crop of 165 million 90-pound boxes. Ninety percent of Florida's oranges are processed into juice.

This would be nearly 50 percent greater than the freeze-damaged production of last year and the largest crop since 1980, when 146.6 million boxes were harvested.

Florida could produce 213 million to 218 million boxes of oranges by 1995, predicts economic research director Bob Behr of the Florida Department of Citrus. This would surpass the record of 206.7 million boxes harvested in 1979-80.

"There is a lot of concern about the pricing structure and the total juice supply worldwide in years ahead," said Bobby McKown of Florida Citrus Mutual, the state's largest growers' association with 12,000 members.