Pure sugar-cane alcohol has begun flowing through Brazil's service station pumps in a rapidly expanding program that has drawn attention from oil-dependent nations throughout the world.

By the end of this year, according to official estimates, 280,000 Brazilian automobiles will be running on straight alcohol -- with slightly lower mileage than their gasoline counterparts, but much lower fuel costs.

Of this number, 30,000 are converted conventional automobiles (the conversion costs about $400), and the rest are brand new cars, mostly Volkswagens and Fiats, with the bright "ALCOOL" sticker flashing the boosterism with which Brazil has been trying for the last five years to start weaning itself from expensive imported oil.

The Iranian-Iraqi war has brought sudden new fervor to what was already becoming a national alcohol crusade. President Joao Figueiredo and many of his aides drive alcohol cars, and experimentation had already begun on alcohol-powered armored cars, airplanes, farm generators, helicopters and outboard motor engines.

The war deprived Brazil of 400,000 barrel per day of imported Iraqi oil -- half of Brazil's total oil imports, which account for 80 percent of the nation's needs. Reserves in storage and increased exports from other countries have forestalled major problems, but the price of gas shot up 18 percent, all gas stations were closed on weekends, trucks were ordered to travel only with full loads, and there is talk now of pushing for an all-alcohol automobile fleet not by the end of the decade, as originally planned, but by 1985.

The alcohol program was unveiled to a dubious public just two years after the 1973 oil price increase added huge expenses to the Brazilian economy. Now motorists, faced with $3 per gallon gasoline and four month waiting lists for alcohol cars, are said to be illegally converting their engines to take the $1.50 per gallon alcohol. Some gas stations selling gasahol, the 20 percent alcohol mix that will power conventional engines, have been caught mixing 40 percent alcohol in to save money, which plays havoc with a gasoline engine's timing.

In good cropland like the flat red soil around Ribeirao Preto, the sudden lure of sugar-cane is making the first of what could become profound changes in agricultural landscape and economics not only for Brazil but also for the smaller nations like Costa Rica and the Philippines, which reportedly have already begun negotiating for distiller equipment of their own.

If the idea ever caught on, it may spread to the United States, where any major alcohol program would probably have to come mostly from corn and grains.

In Sao Paulo State, the rich swath of Brazil that stretches south from Ribeirao Preto, the number of hectares planted in sugar cane have doubled within the last five years, according to government figures. In a nation where drought and intense export cultivation have forced non-export crops such as rice and beans (the staples of the poor) to either drop or barely hold their own, national cane production has increased by almost 50 percent.

Ribeirao Preto's Santa-Elisa plant churns 15,000 tons of fresh-cut cane per day into bubbling vats. The men work 12-hour shifts, 24 hours a day, and still the trucks heaped with cane line up outside in the heat, waiting to unload.

There are dozens of other distilleries making alcohol in Brazil and authorities have approved 285 more for government financing so generous that in some cases the low interest rates amount to subsidies. In the north, on a site reportedly purchased from a consortium that included the Rockefeller family and ARCO chairman Robert O. Anderson, the ground is being cleared for the biggest alcohol distillery in the world.

All these distilleries will probably need far more cane than Brazil grows today. Even though sugar and coffee have traditionally been the nation's largest, export crops, the growing need for alcohol may eventually lead to a sharp increase in sugar cane croplands here at the expense of other crops. This in turn may force food prices upward.

The decision to turn to energy crops to fuel "is certain to drive food prices upward, thus leading to more severe malnutrition among the poor," argues Lester Brown, of the research institute Worldwatch. In effect, the more afluent one-fifth of the population who own most of the automobiles will dramatically increase their individual claims on cropland from roughly one to at least three acres, further squeezing the millions who are at the low end of the Brazilian economic ladder."

Brazilian officials and sugar men tend to scoff off the food-versus-fuel warnings, saying cane and manioc, the root vegetable that also shows great promise as an energy crop, can be grown on the millions of hectares of uncultivated Brazilian land.

Besides, there is no chance that Brazil will ease up on what looks like a way to reduce its staggering foreign debt. Alcohol will not free Brazil from imported petroleum. But by 1985, the nation hopes to reduce its oil imports from 800,000 to 500,000 barrels per day, with the equivalent of another million barrels per day coming from hydroelectric power, Brazilian oil and alcohol.

"The car company that doesn't make alcohol cars right now is going to drop from the market," a Riberao Preto engineer said. "Next week I'm getting my alcohol car. A Ford."