Like Bob Bergland, John R. Block of Illinois is a genuine farmer, a grassroots Midwesterner and a certified nice guy.

But there the similarities end between the present secretary of agriculture and the man named yesterday to succeed him.

In his first public statements yesterday, Block made clear that he wants the Department of Agriculture to be the representative in Washington of farmers and of agricultural businesses. This is the traditional role for the agency but the policy accent changed under Bergland, who sought to make it more reponsive to the needs of consumers.

Bergland took the view that a bridge between farmers and consumers was essential because as food prices rise and political pressures to control farm prices mount, both groups have a mutual interest in economic stability. Bergland's department therefore frequently took pro-consumer positions on issues of food safety, nutrition and grain reserves but argued that these positions were in the long-term interest of farmers.

Yesterday, however, Block said that the department should be "a strong spokesman for agricultural industry," because "the best thing for consumers is a good healthy agriculture." This is a phrase that frequently was used by a onetime Republican secretary of agriculture, Earl L. Butz, an unabashed apologist for the interests of farmers over the interests of consumers.

Unlike the views of Butz, who was a university professor, Block's ideas have been forged by his own experiences as a highly successful large-scale farmer. In many respects, in fact, Block typifies the new breed of men who now produce most of the nation's food. These producers are businessmen and managers as much as farmers, and they are as adept at land transactions and banking as they are at deciding what crops to plant and when.

Block expanded a few hundred acres of his father's land in Illinois into a big commerical farm through shrewd investments. He and partners also purchased and resold a tract of land in Minnesota -- a transaction that has raised questions whether Block was a land speculator.

He dealth with this forthrightly yesterday, saying that the land had been resold only after it had proved too hard to manage.

"Anyway," he said, "people have a right to buy and sell land . . . And I'm a neighbor. I'm from Illinois, not from Saudi Arabia."

In one respect, Block does differ from most farmers. He was educated at the U.S. Military Academy, and takes his place as the second man in Reagan's Cabinet, after Alexander M. Haig Jr., to have attended that institution.

Block's farm manager, Jim Swise, says this has stood his boss in good stead. "I might get mad if one of the hands messes up, but not Jack," says Swise. "I guess he learned how to handle people at West Point."

Block spent only the required two years on active duty before returning to start the job of expanding the family farm, but says that the leadership skills learned as an officer in the 101st Airborne Division helped him when he was tapped to become director of agriculture in the Illinois state government.

Associates describe Block as a man who combines the energy and bearing of a military man with the straight talk that appeals to farmers. Some of this blunt talk has already come through in public statements and interviews. For example, Block has declared that farm price supports are too low, though he hasn't said what they should be. And yesterday he laid out a straightforward view of the connection between food and foreign policy.

"Food is a weapon but the way to use that is to tie countries to us. That way they'll be far more reluctant to upset us."