Agriculture Secretary John R. Block yesterday denied reports that the Reagan administration is preparing to sell large amounts of government-owned corn as a revenue-raising measure.

Block acknowledged that the Office of Management and Budget is interested in unloading about 250 million bushels of corn obtained by the Commodity Credit Corp. after President Carter in 1980 imposed a partial embargo on grain shipments to the Soviet Union.

The secretary said the Department of Agriculture is working on a plan to dispose of the grain. But, he added, "I don't intend to dump the corn. We are looking to sell it on strength and we won't sell any large amounts until we see some strength in the market."

The issue was raised yesterday by Rep. Pat Roberts (R-Kan.), a member of the House Agriculture Committee, who wrote to OMB Director David A. Stockman expressing concern that the budget agency was pressuring USDA to unload the corn.

Roberts said that various USDA officals, including Block, had indicated to him that the department was under pressure from OMB to sell the corn, which, at $3 a bushel, would bring in some $700 million and save yearly storage costs of about $70 million.

Roberts said that he would take issue with any government move that would depress comprices.