America's capacity to feed itself is blowing away

''America is washing out and blowing away!'' So warns Sen. William L. Armstrong (R) of Colorado. That is why he has introduced legislation to stop government support payments for farmers who cause serious erosion problems.

His measure is controversal among soil experts and not too popular with farmers. But there is little disagreement with his basic concern over loss of North America's rich topsoils.

US Department of Agriculture (USDA) figures document that loss. According to the 1981 Resources Conservation Act report, the nation's 413 million acres of cropland currently lose 2.82 billion tons of soil per year to water and wind erosion. That's an average annual loss of 6.8 tons per acre.

This represents a net loss of some two tons after allowing for topsoil formed naturally. The USDA estimates that, under normal conditions, no more than ''four or five tons of soil per acre can be lost annually without damaging the soil's productive potential.''

Senator Armstrong says his bill on prevention of soil erosion is urgently needed because ''we must stop paying farmers to destroy our nation's soil.'' His aides report that, in Colorado alone, landowners seeking quick profits from support programs have converted over 450,000 acres of fragile grazing land to easily eroded cropland since 1979.

The result, warns Armstrong, is that ''we are creating conditions whereby a new dust bowl could occur.'' In some cases, newly plowed Western land has lost as much as 160 tons of soil per acre in a single storm - or more than the one-inch-thick layer formed over a period of one to two centuries.

''Instead of giving farmers an incentive to protect our most precious agricultural resource, our topsoil, the federal government is encouraging farmers to plow up marginal land that is most erosion-prone,'' Armstrong charges.

He says his bill would provide ''statutory authority to deny federal subsidies to crops produced on newly plowed land.'' To many farmers and their congressmen, this sounds like a first step toward government dictation of how farmers should manage their own private property. The senator explains that his ''sodbusters'' bill ''won't tell farmers what they can and cannot do on their property'' but simply ''get the government out of the business of financing erosion with tax dollars.''

Such suggestions that the government not only subsidizes farmers, but subsidizes poor farming, are multiplying now that government farm support payments are expected to top $11 billion this year. This antifarmer reaction is understandable but wrong, says Peter Nowak, an Iowa State University sociologist. He warns that ''we are not going to legislate ourselves out of this mess.''

Dr. Nowak notes that 40,000 tons of valuable topsoil wash into the Mississippi River every hour. He says one reason for this is that ''we are portraying the farmers as villains when in fact they are the victims.'' Instead of legislation to force farmers to adopt soil-conserving measures, Nowak calls for increased federal research and education efforts.

First, develop proven soil conservation practices which will save money for individual farmers, he says. Then beef up the national network of USDA workers responsible for encouraging farmers to try out new soil-conservation measures voluntarily.

The man caught in the middle of the controversy is a young Missouri hog-and-grain farmer, Peter Myers. An advocate of voluntary soil conservation practices, Mr. Myers was picked by Secretary of Agriculture John Block this year to head the USDA's Soil Conservation Service (SCS). He is responsible for coping with US soil and water conservation problems while trying to cut back sharply on the SCS's $1 billion annual budget.

Admitting that ''it would take billions of dollars to straighten out the soil situation,'' Myers says that, rather than ask for more money for SCS programs, he is accepting a 20 percent cut. ''We could raise the biggest ruckus and we wouldn't get more money,'' he explains, ''because the money isn't there.''

According to the USDA's own experts, however, this is no time for cuts. The 1981 Resources Conservation Act report concludes that ''conservation problems threaten to reduce agricultural productive capacity and increase production costs.'' Specific USDA findings are that:

* ''Much agricultural land is eroding faster than the soil can rebuild itself through natural processes. Unless corrective actions are taken, the acreage of this excessively eroding land will increase further.

* ''Floods threaten human life, property, livestock, and crops in upstream watersheds. The likelihood is for greater damage in the future.

* ''Depletion of ground water threatens the continuation of irrigated agriculture in extensive areas of the West.

* ''Deterioration of water quality limits potential use of water for irrigation, municipal and industrial supply, fish and wildlife habitat, and other purposes.''

Under Agriculture Secretary Block's ''preferred program'' for dealing with these problems, ''The highest priority is reduction of soil erosion to maintain the long-term productivity of agricultural land. The next highest priority is reduction of flood damages where risks are highest in upstream areas. Water conservation and supply management, water quality improvement, and community-related conservation problems have next priority.''

Block and Myers plan to accomplish more conservation with less federal money by ''targeting'' funds on critical areas. They also hope to encourage greater participation and spending by state and local governments and by private landowners.

Myers says he is convinced his new program will save money by switching the emphasis away from massive and expensive solutions for soil and water problems toward teaching individual farmers to practice conservation tillage, minimum tillage, or even ''no till'' farming.

He explains that he hopes more farmers will cut soil loss the way he has cut it on his own 1,100-acre Missouri farm. Given increased SCS encouragement, he hopes more will abandon the moldboard plow, which breaks and turns the soil, leaving it vulnerable to erosion. Myers favors leaving crop residue on top of the soil to protect against erosion. The new crop then is planted through this soil-saving layer of ''trash.''

But not even the USDA's recommended ''upper funding level'' of more than $1 billion a year, coupled with rapid acceptance of new conservation tillage methods, would offer a complete solution. Even if the USDA's full recommendations are funded and then accepted by farmers, according to the USDA's own report, ''The loss of soil and water resources will be slowed but not reversed. Implementing a program to reduce degradation of soil to tolerable limits would be prohibitively expensive.''

Myers describes his task as teaching farmers ''to hold the soil in place'' to maintain their land's money-earning productivity. He recognizes the risk of government regulation if he fails to sell fellow farmers on voluntary conservation practices. ''Then, as I tell them, we are going to have more government regulation, which is something as a farmer I don't ever want,'' he observes.

Yet even SCS chief Myers accepts that there may be a need for some degree of ''cross-compliance.'' That means introducing regulations to cut off federal support payments except for farmers who comply with soil and water conservation plans drawn up by SCS technicians for each individual farm unit.

To make cross-compliance more palatable to suspicious farmers, Myers is providing SCS officials with new tools.

For example, the service's district conservationists can access a computer network to study a farmer's current practices. A printout, arranged like tennis-tournament results, graphically displays the costs and probable benefits of switching to a wide variety of soil conservation practices.

Myers showed a typical USDA printout for an Illinois corn-soybean-wheat operation which was listed as losing an average of 40.4 tons of soil per acre each year. A simple shift to conservation tillage promised to cut soil loss to 27.7 tons per acre, at a cost of $8 per acre. Complete corrective measures, according to this USDA plan, would use a combination of no-till farming, contour planting, crop rotation, strip cropping, and winter cover. These promised to cut soil loss to 4.2 tons per acre at a cost of $26.09 per acre.

Even greater erosion control would come from turning the land into pasture. Soil loss would be just 0.3 tons an acre. But the computer printout also showed the cost for this high-yielding Illinois cropland - $126.80 an acre in lost earnings.

Myers admits that the alternative to voluntary soil conservation is probably government intervention. This is because of the ''off-farm effects'' of soil loss. As well as silting up waterways, soil can carry with it large amounts of fertilizers and pesticides. Among other things, current levels of erosion every year fill US waters with an estimated $18 billion worth of nitrogen, phosphorus, and potassium. These are vital fertilizer components which cost farmers more every year to replace.

But soil scientist B. L. Harris, of Texas A & M University, doesn't see either friendly persuasion or government regulation as the answer to America's conservation challenge. He says that good farmers practice soil conservation measures voluntarily. ''No farmer is going to stay on land that is wasting away, '' he notes. Farmers, he explains, ''know what they have to do to protect their land.''

Mr. Harris says that three bad years in a row and heavy farm debts have forced many farmers ''to plant fence row to fence row'' and strain their land's carrying capacity. One result is increased erosion problems. He advises against pushing farmers into trying out promising but untested conservation tillage. Instead, he says, ''We can take the technology we have at present.'' He adds that ''if we applied this known technology, we would increase agricultural production tremendously. I can show you thousands of acres that are ineffectively used.''

At a time when world food needs are being driven up by population pressures, Harris says that instead of reducing agricultural productivity, America needs to protect its best agricultural land and apply the best soil and water conservation practices. The key to this, he says, is simply to ''get the farm commodity prices back up to where they were five years ago. Then farmers will be looking for an opportunity to get tax breaks on improving their land.''

Instead of using either government persuasion or coercion, Harris says, ''increase the price of agricultural products, because if the farmer is making enough money, he is not going to squeeze the last drop out of his soil.''

Former Agriculture Secretary Bob Bergland doesn't agree that better farm incomes will solve the soil problem. ''We hear that if only prices were higher, farmers could afford better soil conservation programs,'' he explains. ''But I've never seen any willingness on the part of farmers to reduce acreage when prices are high. Instead, they tend very naturally to plow up marginal land to increase their production and take advantage of the higher prices for their products.''

Like many ground-level government officials caught in the middle, Marion Porter, an SCS area conservationist, sees some truth in both arguments. He agrees that farmers need better prices for their crops - and that farmers do rip up marginal land to cash in when prices are high.

His solution is to switch from announcing each year's price supports at planting time to setting supports for the next five years. This would be a way, he argues, to give farmers the longer planning horizon needed to invest in soil conservation.

Tomorrow: Conservation could break the bank