What the left hand of government gave farmers in 1982, the right hand now is taking away.

The Agriculture Department is trying to get corn and sorghum farmers to pay back about $240 million of subsidy payments -- overpayments, actually -- that it advanced to them in a controversial political gambit just before the 1982 election.

Although farmers are being required to return the 1982 overpayments, they will not be charged for using the money until now -- a congressional stipulation that will cost the Treasury more than$50 million in lost interest.

The $240 million was part of the federal "deficiency payment" program for farmers, which pays them a direct subsidy to help cover production costs when market prices fall below a predetermined target level.

The advance payments were computed on projected 1983 market prices, but drought and the federal crop-reduction program helped push actual prices above the target levels. This meant that the Department of Agriculture overpaid corn growers by $292 million and sorghum producers by $23 million.

According to Richard W. Goldberg, deputy undersecretary of agriculture, about $70 million of the corn money and $7 million of the sorghum money had been repaid to the department before the collection program began this month.

The department's main collection device is to offset the farmers' 1982 debt from payments they are being given in advance of next year's harvest, another political step aimed at encouraging reduced planting and putting cash in farmers' pockets before the election.

Goldberg said a farmer's debt will be deducted from any funds he may be due from any federal agricultural-support program, ranging from dairy and soil conservation to acreage-diversion and advance deficiencies.

Under USDA policy, a new 13 percent penalty will be charged to farmers who have not returned their 1982 payments by the end of this month. Farmer-debtors who are not enrolled in any federal programs, however, will have until next April 1 to settle their accounts, Goldberg said.

In 1982 and again this year, the department came under heavy pressure from farm-state members of Congress to give economically hard-pressed farmers an extra hand by advancing them money for participating in the 1983 and 1985 federal crop-support programs.

Secretary John R. Block announced earlier that the department will advance farmers as much as 50 percent of the money they might anticipate receiving next year from the acreage-reduction and deficiency-payment programs.

The department's repayment program has drawn a protest from at least one farm state official, Minnesota Agriculture Commissioner Jim Nichols, a Democrat, who said the advance payment schemes were "the most blatant attempt to buy the farm vote with taxpayers' dollars in the history of this nation."

Nichols, among others, urged Block last spring to make advance payments to farmers for participation in the 1984 crop programs, a move he said would help producers with immediate cash-flow problems. Block rejected the request.