AMERICA'S "green revolution" may be over.

The intense 30-year industrialization of the nation's farm lands, during which crop yields more than doubled through the introduction of complex harvesting machinery, petrochemicals and genetically engineered crops, appears to be at an end.

"We are bumping against the ceiling of applied technology," reports John Timmons, professor of natural resources at Iowa State University. "Unless we are able to develop new technologies our productivity is not going to go up."

A survey of major crop yields in the last decade shows that, while production has continued to rise as unused farm land is brought back into production, the yields per acre of major grains have dipped and swung in patterns unmatched since the Dust Bowl years of the mid-1930s.

According to the Department of Agriculture, statistics for 1977 show corn and wheat below the yields attained in 1972.

But what is of increasing concern to many agronomists and agricultural economists is that recently developed farm technology may have masked, or even contributed to, serious problems, particularly the decline in the quality of the nation's soil.

The most serious problem, they believe, is increasing erosion, particularly in the Midwest Corn Belt.

Scientists contend that the heavy use of fertilizers has allowed crop yields to stay at relatively high levels. They warn, however, that this could be a short-term effect. Unless topsoil erosion patterns are not corrected, they say, yields will drop considerably and productions costs will increase dramatically.

"We're Going To Be in Trouble"

OTHER MAJOR problems include: increased sedimentation as topsoil and fertilizers run off into streams and reservoirs; depletion of irreplaceable supplies of ground [WORD ILLEGIBLE] in the Missouri Basin and sections of Texas; compaction of soil through use of heavy machinery, and use of high-quality farmland for urban development.

"We've been generating tremendous productivity," says Timmons. "But if we continue to interfere with soil and water quality we're going to be in trouble."

In a report to Congress last February, the General Accounting Office warned that, because of excessive erosion, farms in the Great Plains, Corn Belt and Pacific Northwest are losing topsoil at a rate which threatens productivity.

Topsoil is crucial to crop production because it contains most of the organic matter and a major share of the nutrients required by plants. Topsoil thickness varies from a few inches to several feet. Corn Belt lands have a topsoil thickness of 6 to 16 inches.

As a general measure, scientists say losses of 5 tons per acre are acceptable in areas of good quality soil. But in a random study of 283 farms, the GAO found that 83 per cent had losses higher than that. Some farms' losses ran two to three times that rate.

The GAO found that the Department of Agriculture's soil conservation programs, costing several hundred million dollars per year, have been ineffective in establishing enduring conservation practices and in reducing erosion to tolerable levels.

The GAO quoted a report by the Council for Agricultural Science and Technology (CAST) which indicated that Corn Belt farmers were less effective in controlling erosion than they were 15 years ago. CAST, which has its headquarters at Iowa State University at Ames, directs task forces of research scientists and collects and publishes material of interest to the agricultural industry.

The CAST report found that the United States was losing 4 billion tons of topsoil a year in 1972 as compared to 3 billion tons in 1934. Farmers "Plowed Up Everything"

MUCH OF THE BLAME for increasing erosion in the Midwest has been laid to farmers who rushed to get more land into production to take advantage of rising grain prices following the 1972 U.S.-Russia wheat deal.

The CAST report estimated that, between 1973 and 1974, 51 million acres were taken out of the federally subsidized soil bank program and converted into crop land. Much of this acreage, known as the "fragile lands," was planted without soil preparation.

Soil losses as great as 50 tons per acre occurred in south Iowa, and erosion of as much as 200 tons per acre was recorded on the sloping cultivated fields in Illinois.

"It was a shortsighted thing they did," says Timmons. "But we got an exhortation from Washington to increase yields, so farmers went out and plowed up everything."

Increased use of fertilizers has allowed a shift away from soil-conserving crop rotations and has allowed farmers to make more intense use of the land through single-cropping or rotating major cash crops such as corn and soybeans.

The GAO noted that, based on the 1974 market value of fertilizers, it would have cost $1.2 billion to purchase the chemicals needed to replace nutrients lost through erosion in that year.

Genetic engineering, the ability to create single strains of fast-growing, reliable food crops, is one of the cornerstones of modern agriculture. But such high-yielding crops also can have little resistance to unforeseen diseases and are often susceptible to pest infestation.In 1970, leaf blight destroyed at least 15 per cent of Iowa's corn crop.

Even the most noticeable facet of the new industrial age in agriculture, the harvesting machines, may have reached their zenith. It appears doubtful that crop yields will be further increased by new machinery.

"Machines are at a very high stage right now," explains Roger Garrett, chairman of the Agricultural Engineering School at the University of California at Davis. "The efficiencies are pretty high; we capture up to 95 per cent of the grain already. It's had to imagine being able to improve upon that."

"Farmers are going to have to take a serious look at our continuing exploitation of resources," says Iowa State's Timmons. "Unless we either change some practices or develop new technology, the windfalls from which we have benefited will be depleted."