President Reagan called agricultural leaders to the White House yesterday in an effort to enlist them in the administration's drive for a more austere farm bill, which remained deadlocked in a congressional conference.

Reagan's meeting with representatives of 16 farm organizations was part of an intensified campaign to force the conferees to adopt a measure that meets White House budget demands.

Agriculture Secretary John R. Block, hefting two five-pound boxes of molding surplus government cheese to illustrate his displeasure with the costly dairy-support part of the conferees' work, flatly said he would recommend that Reagan veto the bill in its present form.

Administration spokesmen said there was not total agreement with the president's insistence on a less costly bill, but said most of the organizations agreed that more congressional compromise is necessary and that passage of a farm measure is essential.

While the president and Block were meeting with the farm leaders, the conferees heard the secretary's veto threat again as they went through another inconclusive session, still at loggerheads on dairy, wheat and feed grain support levels.

House conferees showed no sign of yielding any further, but both Republicans and Democrats took the administration to task for not outlining precisely its "bottom line" on what it will accept in the bill.

Block's general objections to the measure were outlined in a letter to Sen. Jesse Helms (R-N.C.), chairman of the conference. He said that the dairy and grain programs, although closer to his demands than before, could cost taxpayers "billions of dollars" over the next four years.

A key Republican conferee, Rep. William C. Wampler of Virginia, said he doubted the full House would accept a less expensive bill, but he added: "In all fairness, the administration needs to tell us what their bottom line is."

At the suggestion of Sen. Richard G. Lugar (R-Ind.), an effort was being made late yesterday to have ranking conferees meet with Block to get a clearer line on what he and the administration will accept.

But another Republican, Rep. James M. Jeffords of Vermont, a strong advocate of higher dairy supports, said he would consider no more cuts unless they were agreed to "in blood" by the White House. And Rep. Ed Jones (D-Tenn.) complained that the president "has already bled the farmer of all the blood he's going to get."

The House leader, Rep. E (Kika) de la Garza (D-Tex.), said his colleagues had "accommodated the Senate to the extent possible" and, having given in to 90 percent of the administration's demands, now were concerned about their "pride and dignity."

Since the conferees began meeting a month ago, the administration has insisted that they adhere closely to the $10.6 billion Senate version. House delegates, who went to conference with a $16.6 billion package, have agreed to cuts of about $6 billion. The conference measure is now an estimated $681 million above the Senate bill.