ICEBERG LETTUCE prices could give anyone a chill during the bleak days of winter. At $1.25 a head, more or less, some shoppers may opt for butterhead or spinach to fitsalad into winter meals.

The tip on the iceberg situation is this: White flies have hit California's Imperial Valley with a vengeance. They feed on the lettuce leaves, and scientists believe they may transmit a new strain of virus that stunts plant growth, yellows leaves and delays maturity.

The fly comes at a bad time. After two seasons of deflated prices, farmers decided to plant smaller crops this year. Then cool weather hit, delaying maturity and harvest. While prices have come down a little from mid-January highs, the problem won't be solved until researchers figure out if the white fly is truly transmitting the disease, which takes time, and learn more about the new virus.

Nature has dealt a harsh blow in other American crop-growing areas. Jan. 12 brought a freeze that has not only destroyed a number of juice oranges, but decreased the amount of juice in the oranges still on the trees.

It isn't just the Florida freeze that caused a rush of orange juice sales in area supermarkets in the last weeks, says Barry Scher, director of public affairs for Giant supermarkets. "Whenever we have snow or the threat of snow," he says, "it significantly increases the sales of orange juice, bread, milk and eggs." Lately the sales are back to normal, he says, but at a little higher price.

"These things go on all the time," he says of interruptions in food supply. Fresh produce sales and prices are the most quickly affected by price increases, because fresh items are bought and sold daily by telephone for immediate purchase, as opposed to buying future stocks such as canned peas. Supermarkets just buy the same product from a different area, if possible, and price increases may reflect longer shipping distances.

Fortunately, says Scher, "Brazil had a fantastic orange crop this year." Brazilian oranges, unlike many other crops, go toward making frozen orange juice concentrate.

Without further surprises in the weather, the orange juice situation shouldn't worsen, says Bobby McCown of Florida Citrus Mutual, which represents 13,000 citrus growers. Right now, the wholesale price of 12 six-ounce cans of orange juice concentrate is $4.45, a 20-cent increase over the cost of last year's concentrate. "Frankly," says McCown, "it is my opinion that you'll see a stabilizing price" of frozen orange juice concentrate, despite the fact that for the first time in history there have been two consecutive years of freezes during orange season.

An official Department of Agriculture estimate of the total damage to the Florida citrus crop should be released Wednesday.

Still, the imports of concentrate from Brazil should keep the price fairly stable. Whole oranges come from Texas, California and Arizona, and all estimates say those crops remain constant.

The Florida freeze also wiped out perhaps 55 percent of salad crops -- peppers and such. Fortunately, however, Mexico may step in with relief, says Doug Fenley, in charge of the fruit and vegetable service of the USDA's statistical reporting service. Half of Mexico's exports to this country are tomatoes; cucumbers, peppers, eggplant and squash make up most of the rest. Unlike last year's, Mexico's current crops should be substantial enough to keep American prices down.

From Florida, says Tenley, we may get a substantial supply of cucumbers and snap beans in mid-March, but other crops won't recover readily. He estimates smaller production from Florida for the next six months.