It took his public-relations advisers long enough to find the right issue, but they finally came up with some good news that Agriculture Secretary John R. Block could carry out to farm country with trumpets and fanfare.

Insiders had fretted for months over the scarcity of "positive" news for the secretary to report to the Farm Belt, which continues to be gripped by low prices, high interest rates, falling land values and crop surpluses.

They chose the administration's decision to reverse its position on creating a soil conservation reserve as the horse for Block to ride in a one-day streak of news conferences through the Midwest and Upper South.

It worked. Block obtained front-page coverage with his call for Congress to include a conservation reserve in its new farm bill. The secretary said he wanted to pay farmers to set aside up to 20 million of the most highly erodible acres to protect the soil and improve wildlife habitat.

The irony is that only a few months ago, as Block and the administration still were saying that it would cost too much to create a conservation reserve, Congress was moving on its own to write the idea into law.

By the time Block announced his proposal, the House Agriculture subcommittee on conservation, credit and rural development already had included the reserve in its part of the farm bill and the Senate Agriculture Committee was moving quickly in the same direction.

Robert Gray of the American Farmland Trust, which had proposed the same idea more than two years ago at House hearings, took the administration's change of heart with a grain of salt.

"They came out for this after it was a fait accompli, but they got a lot of good news coverage in the Midwest," Gray said. "The only real question was how many acres the reserve would contain -- and both the House and Senate committees have provided for more than Block was asking."

Gray said that he and other soil conservationists are a bit nervous about what may happen after the reserve becomes part of new farm law.

"It's imperative that the private organizations get together and look over USDA's shoulder to keep them honest about the kind of land they let into the reserve . . . . This will be a huge change in the mission of the Soil Conservation Service and the Agricultural Stabilization and Conservation Service."

A NEW LEAF . . . A lengthy political tug-of-war between true-blue Republicans at the department and true-blue Republican Sen. Jesse Helms of North Carolina finally has ended. And therein lies a tale.

Hoke Leggett, a Helms favorite who was No. 2 man at the Agricultural Stabilization and Conservation Service for four years, has left to go to work for the Tobacco Institute, the cigarette industry's lobby..

Because of his long-standing ties to the Democratic Party, Leggett's appointment was vigorously opposed by GOP stalwarts at the department when Helms, chairman of the Senate Agriculture Committee, pushed him for the top job at ASCS.

Leggett's chief connection to Helms stemmed from his efforts to organize North Carolina Democrats on behalf of the conservative senator. Administration political types, fearful of offending Helms, struck a compromise and made Leggett second in command of the ASCS.

But resentment continued apace and earlier this year, as the administration was lining up its team at USDA for a second term, Leggett was unceremoniously bumped into a "special assistant" position and moved to a less commodious office. He joined the Tobacco Institute about a month ago and now will be working with Helms again on new legislation to revise the federal tobacco support program.

NAME DROPPING . . . Economist Terry Barr, a mainstay in the office of the assistant secretary for economics, is leaving to become a vice president of the National Council of Farmer Cooperatives . . . . James D. Boillot, a farmer and former Missouri state director of agriculture, is the new head of USDA's Office of Intergovernmental Affairs. He succeeds Leora Day, who returned home to Idaho.