CHAMPAIGN, Ill. (AP) _ A small army of farm wives, bolstered by the latest cholesterol concerns, prepare to fan out across the country in a lobbying effort touting the health benefits of U.S. soybean oil.

Some of the nation's biggest food producers agree to stop using highly saturated, imported tropical fats like palm and coconut oils in processed foods, following a bristling private ad campaign against the fats.

Meanwhile, major palm oil exporter Malaysia prepares a public relations campaign against what it calls ''vicious scare tactics'' being used against its product.

The vegetable oil war is in full swing.

At stake is the $3 billion-a-year vegetable oil market in the United States, where the dominant domestic soy oil producers are squaring off against foreign competitors such as palm oil.

Soy oil accounts for about 72 percent of the 16 billion pounds of oil sold annually, according to the St. Louis-based American Soybean Association.

U.S. Department of Agriculture figures indicate tropical oil imports have slumped in recent years: coconut oil imports fell 18 percent, to 450,000 metric tons in 1988 from 548,000 metric tons in 1986, while palm oil imports fell 37 percent to 175,000 metric tons from 280,000 metric tons in the same period.

Right now, farmers in the Heartland are benefiting from public concern raised about highly saturated tropical fats. Saturated fats have been linked to an increase in blood cholesterol that causes heart disease.

''The American consumer will be the big winner with healthy food products, and the farmers will benefit too,'' said Gunnar Lynum of the American Soybean Association. ''We represent the good product and we must promote it.''

Tropical oil purveyors see it differently. Malaysia has hired the New York- based public relations firm Hill and Knowlton Inc., which plans a major news conference in March to present scientific claims that palm oil is a balanced fat which reduces cholesterol and has other nutritional values.

The tropical oil producers are facing a foe that has fought their product for some time, via soybean growers and health advocates.

In coming weeks some 1,500 farm wives plan to visit newspapers, radio stations and local groups to tout soy oil. They'll carry cardboard boxes shaped like radios, full of commercial cookies, crackers and cereal that no longer contain tropical oils.

The American Soybean Association, which is funded by roughly 400,000 soybean growers, plans to introduce a ''soymark'' to identify products made with soy oil and has spent $400,000 for promotions over two years.

But one of the more visible efforts is being waged by Omaha businessman Phil Sokolof, who spent $2 million to found the private National Heart Savers Association and has staged a blistering national ad campaign attacking tropical oils as a health danger.

One ad showed a coconut ''bomb'' with a lighted wick and cautioned consumers that their health was threatened by coconut and palm oils. A list it called the ''Poisoning of America'' named popular foods containing tropical oils.

So far, a number of giant food processors - including General Mills Inc., Pillsbury Co., Quaker Oats Co., Kellogg Co. and Keebler - have announced they will drop tropical oils in favor of other vegetable fats in formulas for certain cookies, crackers, and cereals.

Tropical oil producers claim the switching doesn't mean the battle is lost. Rick McElheny, senior vice president of Hill and Knowlton, said the companies made a pragmatic business decision to switch from tropical oils, but predicted they would reverse themselves.

''Because of all this furor and the vicious scare tactics, they don't want to fight that battle,'' McElheny said. ''They'll let us do the education, then come back into the market at another time.''

Some researchers also say the issue is not as simple as the anti-tropical oil ads suggest.

They say a small percentage of saturated fat in the American diet comes from tropical oils - most is from meat and dairy products. They also say some recipes require soybean oil to be hydrogenated and that increases the level of saturated fat.

To lower the risk of heart disease, they advocate a balance between saturated and unsaturated fats in the diet, along with exercise and a reduction in total fat consumption.

''A lot of this is industrial hype - they are worried about the competition for the oil market,'' said Patricia Johnston, a food chemist at the University of Illinois. ''I don't think eating a few cookies with soybean oil is going to make that much difference.''