Americans paid more than twice the world price for sugar this Christmas, under what critics call a sweet deal between Uncle Sam and the nation's sugar growers.

The arrangement has U.S. candy, soft drink and cookie manufacturers -- and their customers -- paying 18 cents or more a pound for sugar. The world price is about 8.5 cents.

The artificially higher price is strongly defended by the nation's 10,000 sugar growers. They say federal help is all that keeps them from being wiped out by unfair world competition.

But critics say the fixed prices are blatant protectionism practiced by the United States. They say the system is a textbook example of "special-interest" legislation devised by lawmakers from sugar-growing states.

The higher sugar prices are costing consumers up to $3 billion a year, or $100 for the average family of four, critics claim.

"It is ludicrous," said Sen. Bill Bradley (D-N.J.), one of the most vocal opponents of the program.

Bradley, joined by several other lawmakers, has introduced bills aimed at cutting the price of domestic sugar. The legislation would also increase sugar imports, easing the rigid quota system the government uses to prop up domestic prices.

The quota system, while complicated, boils down to supply and demand.

The secretary of agriculture is directed by law to guarantee American sugar growers 18 cents a pound. But Congress, although it created the system, has directed that no federal money can be spent to ensure the protected price.

Agriculture Secretary Richard E. Lyng opposes the program, but says his hands are tied. Each year, the secretary must set the quota by computing the ratio of U.S. production to consumer demand, which has been shrinking for a decade.

American producers satisfy the bulk of the demand, and imports are left with the dwindling portion unmet by American sugar growers.

On Dec. 15, Lyng announced that 750,000 tons of sugar will be permitted to enter this country next year, the lowest level in 113 years. The Reagan administration has been required to slash imports by 75 percent since 1984.

Commercial sugar customers, like confectioners, oppose the quota, since it limits their ability to buy cheap sugar.

"It just isn't fair," said Tad Van Leer of Van Leer Chocolates in Hoboken, N.J. The 45-year-old company, which employs 100, has considered moving some of its sugar-dependent production to Canada.

"We don't mind competing, but let us compete evenly," Van Leer said.

The program enjoys the support of a broad congressional coalition of lawmakers with agricultural constituents. In addition to sugar-cane states, such as Hawaii and Louisiana, the system is favored by growers of sugar beets in North Dakota and Minnesota.

Other lawmakers, seeking help for their favorite crops, have also voted to keep the sugar price up.

The coalition has forged an alliance with producers of corn sweeteners, which have all but replaced sugar in soft drinks. Propped up sugar prices have allowed producers of the cheaper corn sweeteners to raise their prices, too.

Even with the government's help, sugar growers say they are unable to make substantial profits.

Eiler Ravnholt, vice president of the Hawaiian Sugar Planters Association, says sugar farmers are getting anything but a guaranteed profit.

Like other farmers, Ravnholt said, cane growers are subject to volatile conditions beyond their control. In Hawaii, just the cost of shipping sugar to the mainland is often enough to eat away profits, he said.

"We're just barely hanging on," he said. Ravnholt said Hawaiian cane growers have cut back their total acreage from 240,000 in 1974 to 185,000.