Bit by bit, the Reagan administration's proposals for a new "market-oriented agriculture," as the conservatives like to call it, are dribbling out and they are setting the stage for a farm-policy donnybrook in 1985.

Agriculture Secretary John R. Block and other administrationofficials are letting it be known that in their efforts to cut the budget, they will propose a 1985 farm bill that would scale back sharply the price-support programs that have underpinned agriculture since the New Deal.

One group, the National Grange, already is criticizing the administration's approach. After one of a number of briefings Block has held for agriculture interest groups, the Grange said the administration is attempting to pit commodity organizations against each other to "cannibalize" the programs.

But the sniping began before Block and others started talking in detail about changes in farm legislation. The stage-setter was a farm-policy slide show prepared weeks ago by the Agriculture Department that sent some farm groups and a few Democrats into a full-scale swivet.

The USDA premiered the show for congressional Republican staffers, a move that so incensed Rep. Charlie Rose (D-N.C.), who was told he could not see it, that he fired off a protest to the department. Block said last week, after a showing at the USDA, that the film will be distributed to USDA offices around the country for showing to anyone who wants to see it.

Its main theme is that present programs are not working and that reform is urgent to avoid more high costs to taxpayers. Critics charge that the show is a thinly disguised promotion for the "free-market" approach that Block supports and a misrepresentation of the programs that have supported farmers since the 1930s.

Democrats already are talking about raising the issue of illegal use of appropriated money for lobbying. But one supporter of the film, U.S. Chamber of Commerce agriculture adviser Stewart Hardy, denied claims that he had placed an order for 300 sets of the show, then added: "I think it's a fair and objective presentation. It takes you up to the brink of endorsing a market-oriented reform . . . and I think it's entirely legitimate for them to do this." ON THE ROAD AGAIN . . .

Don't detour here. It gets better as you roll along. But first, this: the USDA's Office of Transportation held a conference last week in Chicago to give state and local officials insights on finding money to maintain rural roads and bridges.

Said Wesley Kriebel, deputy director of the transportation office: "Rural America needs adequate roads and bridges to meet its transportation needs and to assure that agricultural products move quickly and efficiently from the farm to America's dinner tables. Agricultural townships and counties, however, frequently find themselves financially strained. . . . "

True, no doubt. But then perhaps the USDA did not know about the creative things being done in downstate Illinois. Some farmers who live along potholed country roads in Knox County still are stewing over innovations that local pols are coming up with to get those goodies to the dinner table.

The once-gravel road that leads to the farm home of one of their neighbors now sports a handsome new $100,000 blacktop paving job. And guess whose farm it is. You got it, John Block's. PERSONNEL SLATE . . .

Thanks to the intervention of Sen. Jesse Helms (R-N.C.), Hoke Leggett still holds the second-in-command slot at the Agricultural Stabilization and Conservation Service, which oversees crop programs. Reports here and in North Carolina confirm that Helms, chairman of the Senate Agriculture Committee, put his foot down when ASCS chief Everett (Bud) Rank tried to move Leggett to a new post as a "special assistant."

Leggett, a North Carolinian with extensive ties to the tobacco and cotton industries, got the job in 1981 with Helms' support. Just how long Leggett will stay put, however, is an open question. Sources say he is under investigation by USDA's inspector general on several counts, one involving travel regulations and another involving use of confidential information on tobacco quotas.

Helms also is reported to have told Block that he expects him to retain another North Carolina Republican, former congressman and big-league pitcher Wilmer (Vinegar Bend) Mizell, the assistant secretary for public affairs.

More names cropping up in the speculation over a successor to William G. Lesher, who has resigned as assistant secretary for economics: Marvin Duncan, an official of the Federal Reserve in Kansas City, and Robert Thompson of the staff of the Council of Economic Advisers . . . Vern Highley, who quit as head of the Agricultural Marketing Service to work with the Reagan-Bush campaign, has returned to USDA as an assistant to Block. . . . Arizona farmer John Norton, who served on Reagan's 1980 transition team, is pushing to succeed Deputy Secretary Richard E. Lyng, who is giving up the department's No. 2 job. Norton knows all about federal farm programs. USDA records show that he got 5,255 bales of cotton worth more than $1.7 million and a $36,000 direct cash subsidy for not planting on his Arizona and California farms during the 1983 payment-in-kind program.