Secretary of Agriculture John R. Block reportedly has decided to fire Norman A. Berg, a veteran professional who heads the Soil Conservation Service, and replace him with a farmer-friend from Missouri.

Block's decision, although not yet announced, has drawn strong protests from farm-state legislators of both parties and bitter criticism from a number of soil conservation and farm organizations.

The protests, sources said, have drawn White House attention. Unless Block's decision is reversed, Berg would leave his SCS job on April 2.

The attempted appointment comes as the agency is preparing to carry out the administration's controversial new reduced-budget cropland preservation plan. Berg has been a strong advocate of the plan put forward by Block.

Nevertheless, Berg, head of SCS since 1980 and a career employe at the Department of Agriculture for almost 40 years, would be shunted aside to make room for Peter Myer, a Matthews, Mo., farmer and friend of Block. Myer has no professional conservation background.

Myer's appointment, if it goes through, would make him only the second nonprofessional to head the SCS in its more than 40 years as an arm of the Department of Agriculture.

"I can't fathom the timing," said Neil Sampson, executive vice president of the National Association of Conservation Districts, a farmers' organization. "We will actively resist change of this kind in a professional agency."

NACD joined the National Farmers Union, the Grange, the Society of American Foresters, the American Forestry Association, the Soil Conservation Society of America and other groups in a protest to Block.

Sens. Roger Jepsen (R-Iowa) and John Melcher (D-Mont.), members of the Senate Agriculture Committee, also sent Block a protest last week, opposing a change at SCS for political reasons.

But a spokesman for Rep. William Emerson (R-Mo.), a member of the House Agriculture Committee and also a friend and supporter of Myer's, said an official announcement of the appointment was expected "any day now."