Most of the expensive cars around here -- the Cadillacs, Lincolns and Buicks -- are 1975s, bought with the profits of the last big year in the boom-or-bust potato growing business that dominates northern Maine's Aroostook County.

Often the difference between wealth and debt is close. Many who grew up here, like dentist Don Cassidy, remembers their farmer fathers saying, "If it rains tonight, we'll be millionaires."

For some farmers, the rain fell, leaving them as happy as a man who just filled an inside straight. Tom Houghton, one of Aroostook's major growers, dismisses poker as no kind of risk next to raising potatoes, "This is one heck of a gamble," he said, walking around his huge new potato house while tons of potatoes were being loaded for shipment.

"The potato deal is biggest battle of wits you ever say," says Norman Grant, a local potato broker.

In Aroostook County potato houses today, the talk isn't of making millions, but of cutting losses. Maine's potato business, which everyone here calls "the potato deal" is having hard times.

The late-model fancy cars came not from a "million-dollar rain" in Maine but with the help of too much rain elsewhere.

A hurricane tore up the East Coast in 1975, flooding out potatoes from Florida to New Jersey, but it didn't touch Aroostook. "The boys had a big crop and a big price," Grant said.

Last year's price was a disaster for the growers when they marketed between November and May. This year, the price is just as bad, running $2.50 to $3 for 100 pounds that cost the farmer $4.50 to $5 to produce.

"The next two years are going to be very critical. Perhaps they'll be the most critical in the potato industry's history," said Richard Heath, district director of the Farmers Home Administration.

As potatoes go, so goes Aroostook. The potato crop is so vital and dominant here that schools start in mid-August so that students can work three weeks in the fields during the late-September, early-October harvest.

Heath estimates that farmers are carrying a debt of $2,000 to $2,500 per acre, a burden that for many exceeds the value of their assets.

The FHA makes loans to farmers who cannot borrow elsewhere. "We deal with the higher-risk individuals," Heath said. The agency has about $75 million outstanding in loans to farmers here, he said. Less than 3 percent of the FHA loan volume in the county has been written off, he said, but about 60 percent of the farm loans are now in arrears by one or more payments.

Heath and most growers agree that the principal problem with the potato deal is that the United States grows too many potatoes. Last year's crop was 323 million hundredweight and this year's is forecast at 300 million, although U.S. potato processors and consumers buy only about 270 million hundredweight annually.

"If there was a way to get every grower in the United States to cut back 10 percent, we'd all make a living," said Houghton, who farms 450 acres.

Houghton and other successful growers, however, also consider the FHA part of the problem.

"If they would not loan any more money, well, that would take care of the problem, too," Houghton said, half seriously. "They're doing a lot of good, but they're also doing a lot of harm."

The harm, many of the more successful farmers argue, is that the FHA interferes with supply and demand by supporting the most marginal farmers who are unlikely ever to stand on their own feet. "The guy who owes the FHA the most is the guy who's going to get the next loan," one grower said of the FHA's seeming eagerness to keep its borrowers afloat.

Last year the government appropriated $35 million in emergency funds to buy surplus potatoes. Thus, the critics say, the government was paying marginal farmers to grow potatoes and then buying the surplus.

"If you asked 10 growers, you'll get 10 reasons why the potato deal's no good," Grant said.

Some reasons commonly mentioned include poor potato promotion on the part of the state government, lack of variety in potatto types grown here, rising energy-related costs for growers and too many middlemen.

Idaho growers tax themselves more than $2 million a year to advertise their potatoes, Grant said, while Maine spends less than $100,000 and its independent farmers and shippers use a confusingly large number of brand names, few of which celebrate the state.

Potato men here would like to see the word "Maine" preceed potato as naturally as it comes before lobster.

Most of Maine's potatoes since the 1850s have been of the round and white variety, which have a 90-day growing season suitable to Aroostook where winters are long. Most Americans, however, have come to prefer elongated russets, which taste better baked. In addition, the russet's length and shape provide a longer french fry when sliced, so it is preferred by every sort of potato processor except those making chips.

Maine is pinning its hopes on a new type of russet bearing in part the name Beltsville in honor of the Maryland town where it was born in Agriculture Department laboratories.

The "Belrus" grows quickly enough to be harvested before Aroostook's fields freeze.

Maine used to lead the nation in potato production, but its productive acreage has fallen from more than 200,000 two decades ago to 115,000 and both Idaho and Washington state produce more potatoes now. With distaste, Grant remarked that irrigation of dry soil is so successful for potatoes that Nevada now harvests 20,000 acres of potatoes annually.

Potato farmers in other states suffer as much as Maine's from low prices, but they have more potential uses for their land, people here believe. No alternate crop has succeeded in Aroostook, including sugar beets, which proved a spectacular failure in 1976 when a federally funded, $22 million processing plant closed.

The Maine market has been complicated by problems on the New York Mercantile Exchange, which most recently suspended potato futures trading temporarily last March because of irregularities.

Farmers can take some of the gamble out of the potato business by hedging their bets on the exchange, but Houghton and some others have no confidence in its. "Someone is always trying to rig something," Houghton said. "It's the supply and demand of the money, not the crop, that sets the Mercantile price."

As a broker who trades on the exchange, Grant disagrees strongly, but he and Houghton are equally bearish about potatoes.

Houghton said he has talked to growers along the East Coast and hasn't found a single optimist. "I wouldn't be long on anything potatowise," Grant said. In the long run, however, Grant sees good times coming. The rising cost of transportation is going to give Maine potatoes a significant advantage in the huge Boston-to-Washington market, he said.

"The day is coming when the East is going to feed the East and the West will feed the West," Grant said.

That would mean a lot of new fancy-model cars in Aroostook again as the Maine potato climbed to new heights.

The most recent soaring by Maine potatoes brought no grower a nickel. When Double Eagle II took off on the first successful transatlantic balloon flight from nearby Presque Isle in August 1978, it carried sacked potatoes as ballast.