Driving past the hilly grasslands along US Route 40, Harry Kravig points out a distant landmark. ''You see that (grain) elevator?'' he asks his passenger. ''From that elevator north is real good wheat land.'' But the land this side of it, ''this land right here, I would say, is very, very marginal.''
Mr. Kravig, a longtime wheat farmer and cattle rancher, stops his blue pickup truck to take a closer look. Here, a few miles west of Hugo, Colo., the grassland is bare in spots - even with the good rain this year. Farther up the road, farmers have plowed up the marginal land to try to grow wheat.
Kravig and a good many other farmers, are worried about the environmental impact of plowing up fragile grassland in the Great Plains. In eastern Colorado alone, nearly 600,000 acres of fragile grassland are estimated to have been plowed up between 1978 to 1983 for dry-land wheat production.
''I hate to see all the grassland broke up as much as any man,'' says Bill Monks, a farmer in nearby Limon, Colo., in a telephone interview. ''I'd rather run the cattle if there's money in it.''
But ''there's no money in cattle,'' Mr. Monks says. He has two sons who, like many ranchers on the Great Plains, have switched to wheat in an effort to stay on top financially.
So far, the weather has cooperated. But agriculture officials worry that a few dry years could set the stage for heavy wind erosion reminiscent of the Dust Bowl.
To counteract this, Congress is considering measures that would make government programs - price supports, crop insurance, federal loans, and disaster payments - unavailable on newly plowed fragile land. The Senate version would restrict payments only on crops planted on the erodible land. The House version would deny all payments to any farmer who plowed up the fragile land.
But neither farmers nor agricultural economists believe these measures will stop the so-called plowout.
''I don't think that this bill will do the job,'' says Kravig.
The main incentive for the plowout does not appear to be government payments, adds Paul C. Huszar, agricultural economist at Colorado State University in Fort Collins.
Recently, Mr. Huszar surveyed ranchers and farmers in Weld County, Colo. And from the preliminary results, he says, decisions on plowout were swayed most by the relation between beef and wheat prices. The beef industry is so depressed right now that farmers are turning to wheat, he says, even though that market is glutted, too.
Another important plowout incentive is the expected land appreciation. Many lending institutions urge farmers to plow in order to improve the value of their assets, according to the survey. Plowed cropland is generally worth much more than range land.
Around Hugo, for example, Kravig estimates an acre of marginal land might sell for $100 to $150 as pasture - but $250 to $300 when plowed.
Government programs may play an indirect role in plowouts, since lending institutions might perceive a farmer's access to government programs as a way to reduce the risks of farming, Huszar says. Government programs also help to exaggerate the advantage of wheat over cattle by supporting wheat prices while not supporting beef.
Still, Huszar concludes from his survey, the availability of government programs - such as crop insurance, disaster payments, price supports, storage loans, and Farmers Home Administration loans - was the least important factor in the decision whether or not to plow.
Weld County has taken local measures to discourage plowout by requiring permits of would-be sodbusters. The ordinance ''slowed it perhaps, but it hasn't stopped it,'' Huszar says of the sodbusting in the county.
He suggests an alternative: ''Instead of providing penalties for plowing, maybe we should provide rewards for conserving.''
The costs of paying ranchers to keep their land in grass might be offset by future government reseeding and other conservation programs. And such payments might only have to make up some of the difference between the financial rewards of wheat and livestock farming. ''Ranchers are not really anxious to get out of ranching,'' he says.
How big is the plowout problem?
Officials with the US Department of Agriculture (USDA) admit they don't yet know. Some crucial 1977 data must be revised before they can calculate the net land conversions.
Nor is this the first time plowouts have occurred in the Great Plains, notes Ralph Heimlich, an agricultural economist with the land branch of the USDA's Economic Research Service. ''In the '30s, the '50s, and to some extent, the '60s , government has had to step in to take over the (marginal and eroding) land.''
Kravig, for example, can still point out grass-covered fields that were once under cultivation in the '30s and the '50s. About 25 years ago, he reseeded two sections of plowed up land himself to raise cattle.
He bemoans the fact that investors and large operators are taking advantage of the situation and buying up land. But, he says, a landowner should be free to choose how he he uses the land, as long as it doesn't hurt his neighbor. ''Maybe it's part of a cycle,'' he adds. ''Who's to say that it won't be grass some day?''
LAND EROSION Cropland farmed in 1982 (in millions of acres). HIGHLY POTENTIALLY ERODIBLE ERODIBLE* Colorado 4.4 16.0 Kansas 2.8 8.8 Montana 3.8 16.6 Nebraska 3.8 15.6 North Dakota 2.4 3.8 South Dakota 1.6 9.3 Wyoming 0.8 13.4
*Pasture and rangeland that would be highly erodible if converted to cropland.