CHICAGO, JAN. 11 -- Amoco Corp. was ordered today to pay $85.2 million to France and about 90 other plaintiffs for damages suffered when the supertanker Amoco Cadiz ran aground off the Brittany coast a decade ago, spilling 68 million gallons of oil.

U.S. District Judge Frank McGarr had earlier found Amoco and a Spanish shipbuilding firm, Astilleros Espanoles S.A., liable for damages resulting from the March 16, 1978, accident that sent wave after wave of thick crude oil washing up on 100 miles of beaches.

The case was heard in Chicago because Amoco is headquartered here, but McGarr was required to apply French law in determining the award because the accident occurred there.

The French government had sought $466 million and the other plaintiffs a combined total of $695 million.

But McGarr said he found the claims by the plaintiffs, which included villages along the idyllic northern coast of France as well as environmentalists, oystermen, fishermen, businessmen and property owners, to be greatly exaggerated.

"They reasoned {that} the best way to get what they were entitled to was to ask for three, four, five times what the claims should have been -- and that's what they did," he said.

Attorneys for Amoco Corp., and all the plaintiffs except the French government, said they planned to appeal. Attorney Benjamin Haller, lead counsel for France, said he would fly to Paris to confer with government officials about whether to appeal.

McGarr said about four-fifths of the judgment would go to the French government because it already paid most of the bills for the cleanup.

About $39.7 million of the judgment was interest payments. The award does not include court costs, which also will be borne by Amoco.

"The townspeople will be very disappointed," Adrien Kervella, mayor of Saint-Pol-de-Leon, a village of 8,000 on the Brittany Coast, said through an interpreter.

Officials of 10 French villages attended the courtroom session.

"Our objective was to make the person who caused the damage pay, and I think they must pay -- even though they said they didn't do anything," added Kervella.

Countered Frank Cicero, Amoco's lead counsel in the case: "We think the objective may have been to make Amoco foot the bill for every public works project {in the Brittany villages} for the last 10 years -- and maybe even future ones."

Cicero said Amoco, the nation's fifth-largest oil company with 1986 sales of $20 billion, will appeal both the judgment and the finding of liability in the first phase of the case.

McGarr ruled that Amoco was responsible for seeing the entire judgment paid.

Amoco and Astilleros are disputing how much liability each should bear and the judge said he would determine what percentage should be borne by Astilleros.

The Spanish firm, located in Cadiz and reputed to have built the caravels on which Christopher Columbus crossed the Atlantic, already has a judgment entered against it and has refused so far to recognize the jurisdiction of U.S. courts.

Cicero said Amoco would press ahead with its lawsuit, contending that Astilleros was responsible for the design, materials and maintenance flaws that McGarr ruled in 1984 caused the accident.

The supertanker had been foundering just two miles from the coast, rudderless and facing hurricane-force wind.

A tow line attached to the ship in an effort to halt its drift towards the coast snapped and the tanker smashed on jagged rocks close to the small fishing village of Portsall.

The spill created a slick 18 miles long and 80 miles wide.

Today the beaches are clean and the wreckage of the ship is no longer visible.

But ecologists debate whether the region's famed oyster beds will recover, and bemoan what they say are the changed migratory patterns of birds that departed when the beaches were blackened.

"The activities on the beaches are normal again," said Kervella. "But I will have a hard time going to the town meeting and explaining to them the sense of this judgment."