Richard E. Lyng, President Reagan's choice for secretary of agriculture, breezed through a Senate confirmation hearing yesterday that sometimes took on the air of a Woodstock-era love-in.

Republican and Democratic members of the Agriculture Committee welcomed the imminent return to public service of Lyng, 67, a veteran Washington hand who twice has held high Agriculture Department positions.

Several offered "condolences" at his decision to take the high-pressure USDA job as U.S. farmers face their most trying economic time since the Great Depression.

Lyng noted that his nomination had brought other messages of condolence "because of the impossible economic condition of agriculture." But he said, "Things are going to get better, they are going to get better just when some people will think it's time to give up."

Approval of his nomination by the committee, and eventually the full Senate, appeared certain, although Chairman Jesse Helms (R-N.C.) gave no indication when it would go to a final vote.

Lyng, who would be the first agriculture secretary from California, was deputy secretary during Reagan's first term but resigned to set up an agricultural consulting firm last year.

He headed the state agriculture department in California when Reagan was governor there and from 1969 to 1973 was an assistant secretary of the USDA. From 1973 to 1979 he was president of the American Meat Institute.

Lyng, who seems as popular on Capitol Hill as a favorite uncle, promised the committee that he would make increased farm exports his top priority at the department. But he promised few other changes in administration farm policy.

He told Sen. Edward Zorinsky (D-Neb.) that the main difference between himself and former secretary John R. Block, who resigned in January, would be "more in style than in substance."

Lyng also pledged that he would "do what is possible" to see that money is available from the Farmers Home Administration to meet the heavy demand by farmers for spring planting loans. But he held out little hope that loan funding would be increased.

In another sequence of questioning on farm economy issues, Lyng refused to walk into a rhetorical ambush laid by Sen. Tom Harkin (D-Iowa), who wanted to know if agriculture's real problem is too many farmers.

Lyng said he didn't think so and also took issue with an estimate by the American Bankers Association that economic pressures would force at least 100,000 farmers out of business this year.

But Lyng rejected a Harkin proposal to help farmers through their spring financing crunch by offering them advance price-support loans on crops harvested in the fall.