A leading House Democrat accused the Reagan administration yesterday of "playing games" with next year's budget by underestimating the cost of farm price supports by some $5 billion.

"At some point it would be nice to present the facts as they are," Rep. Leon E. Panetta (D-Calif.) told Agriculture Secretary John R. Block. "I'd like to see you at least give us something that has more honest figures."

Panetta suggested that the administration intentionally underestimated probable expenses of the Commodity Credit Corp. (CCC) to keep the deficit from looking even higher than the $91.5 billion the president has projected.

The scolding by Panetta was just one of a number that Democrats and Republicans alike administered to the secretary as he appeared before the House Agriculture Committee to outline his 1983 budget.

At $23.5 billion, the Agriculture Department's spending plan is about 20 percent less than this year's.

One farm-state legislator after another lashed out at the secretary for proposed budget cuts.

It was a sharp contrast to last year's sessions, when the committee grudgingly went along with most of the administration's demands for reduced agricultural spending.

The different tone stemmed largely from a drastically altered economic outlook that gives the legislators election-year nervousness about severe recession on the farm.

With a bumper harvest, continuing high interest rates and inflation, farmers last year had their lowest net income since the Depression era.

Block readily agreed that there are problems on the farm, but he painted a generally optimistic picture for the second half of this year, predicting improvement as the administration's austerity policies take effect.

Most members of the committee weren't buying that.

Rep. Ed Jones (D-Tenn.), for example, told Block that the White House is not getting a true picture of farm-economy problems and "your program utterly fails to recognize the problems that we have."

Rep. Berkley W. Bedell (D-Iowa) said that Block's optimism showed "the administration is not willing to accept reality...you doubt your own economic forecasters."

Bedell recited USDA internal economic projections that foresee net farm income this year of $14 billion--about $2 billion less than the figure that Block customarily cites.

"I'm not aware of those figures," the secretary said.

Responded Bedell: "If they are accurate and you are not aware of them, I'm even more concerned."

Rep. E. Thomas Coleman (R-Mo.) and Chairman E (Kika) de la Garza (D-Tex.) criticized the secretary for proposed heavy new cuts in food-stamp and nutrition programs on top of those already pushed through last year after heated debate in Congress.

"These food-stamp proposals are anti-work proposals," Coleman said.

"You penalize people who try to work. The 18 percent reduction in benefits is a mistake...

"We hit your $2 billion target for savings last year and now you want $2 billion more . This is hard for us to do."

Unlike last year, however, Block indicated a willingness on the administration's part to compromise with the committee on ways of achieving more savings in the food-stamp and other government nutrition programs.

"Our ears are not closed," Block said.

The USDA budget calculates CCC expenditures of $1.5 billion, but Panetta said the Congressional Budget Office figures the commodity price supports and export credit guarantees actually will cost closer to $7.3 billion.

"Every administration plays games with the CCC," Panetta said.

"But you are off by $5 billion--and we're not going to accept that.

"If the estimate is low, we are faced with an additional supplemental appropriation.

"Why in hell can't we be more realistic?"

Block argued that the administration "can err on the other side," but Panetta cut him off at the pass.

"It has never happened," the congressman said. "That's the game that is played here."

The administration's CCC expenditure estimates are based on optimism that dairy farmers will cut back on milk production in a major way and that higher prices for basic farm commodities will reduce the need for support loans and direct subsidy payments.