Warnings echoed that they were going too far, but congressional conferees backed a series of steps yesterday to protect farmers from export embargoes, elevator bankruptcies and economic emergencies.

The big addition to the new farm bill, still several days from completion, was a plan that could cost as much as $30 billion if a major agricultural embargo were declared.

That provision, along with an emergency loan program that was reauthorized, brought new warnings that a final version of the four-year bill will meet additional resistance in Congress and at the White House over money and policy issues.

The conference chairman, Sen. Jesse Helms (R-N.C.), said he was increasingly concerned and that the conferees may have to go back and scale down other program costs.

Added Sen. Robert J. Dole (R-Kan.): "We have to get the genie back in the bottle . . . . We have got to take another look at sugar, peanuts, sunflowers and so forth."

The White House has indicated it wants a bill that costs less than the Senate version, but the conferees have added about $250 million in commodity outlays over the life of the bill, according to the Agriculture Department.

The newest element of budgetary concern arose yesterday with a one-year extension of loan guarantees up to $600 million for farm emergencies, under a proposal by Sen. Thad Cochran (R-Miss.).

The administration's representative at the conference, USDA economist William Lesher, told the conferees they were "adding another problem" to the bill with the extended credit scheme.

Costs of that program, however, would be minimal compared with the potential expense of the embargo protections. Lesher said the administration wasn't concerned, repeating its pledge never to impose a selective embargo on agricultural exports.

But the conferees, recalling similar pledges from the Carter administration before its partial embargo on grain sales to the Soviet Union, were buying no promises.

They argued bitterly among themselves for several days, then yesterday bought a Senate provision that would require loans and direct payments to farmers if any major agricultural embargo were declared for national security or foreign policy reasons.

That action came in the wake of two Senate votes late Thursday on trade embargoes. One would give Congress 60 days to veto any selective embargoes after 1984. The other would authorize a total trade embargo in the event of Soviet or Warsaw Pact military action against Poland.

USDA estimated that the conferees' compensation plan for farmers could cost between $10 billion and $30 billion, but Lesher said no one should worry "because we're not going to have any selective embargo."

Despite his assurances, even Republicans were skeptical. Rep. William M. Thomas (R-Calif.) argued that the language would give farmers a "windfall" and he tried without luck to have the national-security and foreign-policy stipulations stricken.

Another Republican, Sen. Roger W. Jepsen of Iowa, accused Thomas of "trying to pull the wool over peoples' eyes." He said the amendment would strip the provision of meaning. "With this," he said tartly, " Secretary of State Al Haig obviously has done his homework overnight."

Thomas was voted down and the House conferees then voted 10 to 3 for the Senate's tougher language, as Rep. Paul Findley (R-Ill.) predicted it "will rank even higher in urban members' eyes than sugar or peanuts as another reason to defeat this bill."

In another stretching of the safety net for farmers, the conferees accepted an amendment by Dole that would give farmers preferential federal help if they have grain stored in bankrupt elevators. Dole said the problem is growing in the Midwest because court rulings have prevented farmers from regaining access to their grain while litigation goes on.