Agriculture Secretary John R. Block's decision to name a longtime Republican farmer friend as head of the Soil Conservation Service ran into an earth-shaking stormfront in the Senate yesterday.

Appearing before the Appropriations subcommittee on agriculture, Block said he replaced professional conservationist Norman A. Berg with Peter C. Myers of Matthews, Mo., because of a desire to have farmers in top policy jobs.

The secretary praised Berg, a veteran of 39 years with the SCS and head of the agency since 1979.

But he said that Myers knows soil conservation "from a practical standpoint" and will be a good administrator.

The storm broke at that point.

"A little candor would be helpful," said Sen. Thomas F. Eagleton (D-Mo.). "You decided to have a full-time farmer in this job because he's your buddy. You eulogized Norman Berg for 39 years of great service. You thought so well of him that you kicked him in the ass."

Eagleton then queried each of the high-level Department of Agriculture officials flanking Block at the witness table: "Are you a farmer? Are you a farmer?" None could say yes. "What are you doing in your job?" he asked each one.

Sen. Jim Sasser (D-Tenn.) said Block's move set "an extremely damaging precedent" for SCS.

He said the agency's efforts to control severe soil erosion problems in west Tennessee had been well-received and that Berg was highly regarded by farmers there.

"The administration is in trouble with farmers in my state," Sasser said. "This change at SCS is a window-dressing. It is like Boeing firing all its aeronautical engineers and hiring a pilot to design airplanes."

Meanwhile, Eagleton also lectured Block about President Reagan's statement that federal spending for nutrition programs has risen somewhat when actually it has fallen.

"Some people wonder whether we have a vacuous president. At least I do," Eagleton said.

Eagleton said Reagan's contention that federal spending for nutrition programs had risen 4.5 percent was wrong, because spending declined from $16.2 billion in fiscal 1981 to $15.3 billion in fiscal 1982.

Reagan wants to cut spending to $13.3 billion in fiscal 1983.

Last Sunday, Reagan was asked about an advocacy group's statement that further cuts should not be made in nutrition programs because of an apparent increase in the case of malnutrition among low-income children.

Reagan replied that there was not an actual cut in nutrition programs, only a cut in the rate of increase in federal spending.

Block said the president might have been talking about government-wide expenditures; the secretary also said spending on a lot of other entitlement programs has risen. Eagleton was not persuaded.

"People who study these programs are really beginning to smirk," he said.