In past weeks, militant farmers have been swarming like agitated hornets. They have stopped traffic with their tractors, turned goats loose on Capitol Hill, besieged the Agriculture Department and pelted Secretary Bob Bergland with rotten eggs.

Their main gripe is that they aren't getting high enough prices for their crops to make a living. But they have also complained to us of another threat to their livelihood, which has gone largely unnoticed.

Foreign profiteers, the farmers have told us, are buying up American farmland with devalued dollars. Arab, Dutch, German and Italian millionaires have already acquired vast domains all across America and are actively searching for more acreage.

Our own investigation of the farmers' charges indicates a sharp increase in foreign farm purchases. Many acquisitions have been made, we discovered, by dummy corporations set up in the Netherlands Antilles, which are known throughout Europe as a tax haven for siphoning off business profits and unreported income. Dummy corporations are easily set up there. Operating from these palmy, Caribbean outposts, foreign investors are buying land from economically beset American farmers - land their forebears tilled for generations.

In Utah, for example, a combine of Dutch clients has purchased 6,000 acres of prime farmland. This deal was made, however, through California rather than the Caribbean. Local realtors told our reporter Hal Bernton that many Utah farmers are forced to sell because they are unable to keeo up their loan payments and are hard up for operating capital.

A spokesman at Mountain Valley realty of Logan, Utah, told us the same Dutch investors are shopping for another 4,000 acres in the state. They plan to lease the land back to its original owners for another 15 years. In other words, they are more interested in land speculation than farming.

Four corporations, operating out of the Dutch Antilles, have purchased 25,000 acres of cropland in President Carter's home state of Georgia. Foreign investors own at least 150,000 acres in Missouri. And our sources say two Italian tycoons, with a Curacao corporate front, now own 1,920 acres near Dalhart, Texas.

One of Oregon's largest agricultural holdings, Green Villa Farms, has been sold to Dutch interests for $5.7 million. The farm had to be sold, the manager reported, because it was almost impossible to make a decent profit growing cabbage, cauliflower, beans, peas and wheat.

The foreign land grabbers like to keep their operations secret. Missouri's agriculture director, Jack Runyon, told us that a group of Arabs visited a small town in his state last summer. Shortly thereafter, some 1500 acres of lush farmland changed hands. Runyon said other purchases were made by 13 companies in the Dutch Antilles. The true owners are hard to trace, he said.

Prestigious U.S. investment firms also purchase land for foreign investors. Among then is the Doane Agriculture Service, Inc., of St. Louis. The board chairman, Forest Goetsch, told us that five percent of Doane's land investment clientele are now foreigners. Until two years ago. Goetsch said, Germans with Deutschmarks to squander were investing heavily in farms in Argentina and Brazil. Now they are focusing on the United States, he said.

No one knows percisely how much U.S. farmland is owned by foreign interests, we discovered. An Agriculture Department official confessed that there is "no reliable data" on the subject. "We need more information," confided another official, "if we are to avoid making decisions in the dark."

There has been no massive turnover of farm property. According to the Agriculture Department, only three percent of the nation's farmland changed hands last year. But of this, up to 21 percent may have involved foreign investors.

Those involved in the land speculation, furthermore, seldom advertise. As one real-estate attorney put it: "This is a very hugh-hush affair. It is a very lucrative market, and lawyers don't talk about it too much."

But occasionally, a discreet advertisment will appear on the financial pages. One intriguing ad invited foreign investors to a Zurich, Switzerland, hotel on March 21 and 22 for a "confidential" discussion of U.S. land bargains. Stated the ad: "it's no secret international investors are eager and able to buy prime U.S. real estate but often do not have the proper contacts to begin negotiations. Zurich Market Day will bring you together and help establish on-going personal contacts."

It is on ironic that the farmers should be the victims of the decline of the dollar, for they exported as estimated $23 billion worth of farm produce in 1977, which bolstered the dollar. Nor are they at all responsible for the skyrock-eting price of land, which has attracted foreign investors. The cost of land has been driven up mainly by the rapid spread of residential suburbs into the countryside. In the new communities, property taxes have shot up, making it more difficult for the farmers to survive. Federal taxes also make farms good write-offs for the wealthy, who buy farmland.