The Reagan administration, insisting that adequate help is available for farmers, renewed its opposition yesterday to House members' efforts to liberalize federal and private farm credit programs.

Farmers Home Administration (FmHA) chief Vance L. Clark urged a House Agriculture subcommittee to reject bills designed to ease debt and high-interest burdens facing many farmers.

But other witnesses, including congressmen, bankers and farm leaders, told the panel that the prospect of continued low prices means thousands of farmers face foreclosure unless credit relief comes.

"We need a program that is a solution for our farmers -- not simply a bail-out of an institution or a bank," said Rep. Leon E. Panetta (D-Calif.), sponsor of a measure that would allow farmers and bankers to restructure debts and avoid foreclosures.

"We must act now to prevent huge loan defaults that could shake confidence in the nation's financial system, causing interest rates to rise and slowing the growth of income and jobs," he said.

Witnesses representing lending institutions, however, showed only mild interest in the Panetta proposal and one by Reps. Thomas A. Daschle (D-S.D.) and Berkley W. Bedell (D-Iowa) that would provide federal subsidies to lower farmers' interest rates.

"I won't suggest that maybe you're a little greedy," Rep. Lindsay Thomas (D-Ga.) told lenders who insisted that ample credit is available for qualified borrowers. "I hope you will rethink your statements."

The daylong hearing produced a torrent of complaints about lending policies of the FmHA, the Farm Credit System and some commercial banks, which were accused in general of insensitivity toward farmers' financial problems.

Rep. E. Thomas Coleman (R-Mo.) called for the firing of Missouri FmHA chief John Foster, saying he has administered loan programs improperly. FmHA's Clark did not respond to Coleman's demand but conceded that the agency has had problems in Missouri.

Meanwhile, the Federal Deposit Insurance Corp., which insures bank deposits up to $100,000, asked Congress for greater authority to cope with record bank failures, many stemming from bad farm, energy and real estate loans.

FDIC Chairman L. William Seidman told the House Banking Committee that more than 1,200 banks are on the problem list. He asked for legislation to lower to $250 million the minimum size of banks eligible for emergency acquisition under the Garn-St Germain Act of 1982, which expires Tuesday.

Seidman also asked for authority to take over severely troubled institutions as well as the collapsed banks that the law requires. He and Chairman Edwin Gray of the Federal Home Loan Bank Board made the same request last month to the Senate Banking Committee.

On March 25 the committee approved a 90-day extension of the law. Aides say this bill, which awaits a Senate vote, is unlikely to include the regulators' proposals.