IN FLORIDA, where orange juice has long been king, the $3 billion industry is losing its crown jewels. Since 1979, three freezes have devastated trees in Florida orange groves, the last wiping out close to a third of the state's crop. And now, seedlings that it was hoped would eventually replenish those groves are being threatened by citrus canker, a destructive disease that has thus far forced the burning of infected plants in six nurseries.

The Florida Citrus Commission predicts that the canker will not change the supply or price of oranges harvested this season, more than 90 percent of which will be processed into juice. Instead, the outbreak only aggravates an already tenuous situation.

In short, vast and complex changes have been occurring in the Florida orange juice industry, an industry that supplies the United States with 80 percent of the drink. And the gist of it is this: The connection that binds orange juice to Florida like lobsters to Maine is being severed. While orange juice may still be processed in the Sunshine State, nowadays it is a cross-breed, a blend. That carton in the refrigerator case or can in the freezer is a hybrid that includes concentrate from Brazil.

Consider the following supply-and-demand situation: Recent Florida freezes have decreased dramatically the numbers of oranges harvested for fresh and processed use. In 1979-80, the last harvest without a freeze, 206 million boxes of oranges were harvested. Last year, that figure dropped to 116 million. And for this year's '84-'85 season, according to Bill Jones, public relations director of the Florida Citrus Commission, the industry is estimating the orange harvest at between 95 and 110 million boxes.

At the same time, U.S. consumption of orange juice made from concentrate has increased substantially -- in fact, it doubled from 1970 to 1983, a trend that the Florida Citrus Commission attributes to an industry-wide quality improvement program, a massive advertising campaign and more recently, widespread consumer demand for fruit and fruit juices.

So to counter increasing demand with dwindling supply, the Brazilian orange market has been tapped. Since 1977, the United States has been Brazil's major market for frozen concentrate, according to the U.S. Department of Agriculture. In fact, in 1982, according to the USDA, Brazilian imports of frozen concentrate contributed to more than half of U.S. production and nearly half of U.S. consumption. And although that figure fell slightly in 1983, predictions are that 1984 will be another boom year for Brazilian imports.

Brazilian concentrate is blended in the United States with Florida concentrate in varying ratios, depending on the processor, said Tim Clarke, director of corporate relations of Tropicana. Florida concentrate is sweeter than Brazilian, said Clarke, and interestingly, what makes it so are Florida's colder winter nights, which help to crystallize and retain the sugar. Processors can keep concentrate frozen for long periods, although the USDA says that U.S. juice processors do not maintain enough frozen concentrate to cover large shortfalls in production.

So while the extent of the infestation still remains to be seen, the canker's effect on the immediate future of orange juice will probably remain unchanged. But until Florida recovers from it and the past frosts, processors can only look forward to an increasing dependence on Brazilian concentrate, says Ben Huang, an agricultural economist at the USDA. And for the consumer, says Jones of the Florida Citrus Commission, it all means that relief from already-high orange juice prices is unlikely. The August 1984 Consumer Price Index for a 12-ounce can of frozen orange juice concentrate was $1.69, the highest ever recorded.

In the meantime, prices of California fresh oranges (about 75 percent of that state's oranges are sold fresh) remain high. Last week, California valencias were selling for two for 79 cents at Safeway and three for 99 cents at Giant.

The reason, however, has nothing to do with the canker, but with a general nationwide shortage of eating oranges. Besides a total wipeout of Texas' crop -- also due to a devastating freeze -- it is the tail end of a "very short" valencia season, according to Shirley Kirkpatrick of California Citrus Mutual, a trade association. Navel oranges (which are too bitter for juice) aren't harvested until Thanksgiving, she said.

But until the fresh and juice situation irons itself out, this could, says Barbara Ettinger of Safeway, be "the year of alternative vitamin C sources."