Like desert wanderers, they found an oasis in Jane and Charlie Yarn's backyard, nibbling star-shaped canapes, sipping pink lemonade and wine spritzers and pining beneath the magnolias for someone of stature, anyone, to stand up for their birds, their bees and their trees and do battle with James G. Watt.

To these 300 beleaguered environmentalists, who feel they are outcasts in the world according to Reagan's interior secretary, the gentle south Georgia drawl of Jimmy Carter never sounded so good. He had come to deliver a civics lesson in presidential power Friday evening and announce the end of his self-imposed reticence, attacking successor Ronald Reagan's "abhorrent" environmental policies in an angry speech.

With his words rising above a crescendo of crickets, he accused Reagan of "subverting the public will" in dismantling federal laws on environmental quality, hinting at a future role for himself as a point man for America's environmental movement.

"Laws designed to protect the quality of the air, water and land are being circumvented or ignored," he said. "Longstanding programs are being eliminated or subverted by executive order or budget policy. Public lands, forests, and mineral resources are being squandered or sold at giveaway prices. Air and water pollution standards are being lowered by every possible means. Powerful interest groups are being enriched at the expense of the American people."

Moreover, Carter charged, Reagan was guilty of engineering legislative end runs -- "sometimes guilefully" -- as a way around federal court injunctions blocking his policies, in effect, to "subvert the public will."

As an ex-president, Carter was there to remind the environmental leaders that such policies emanate from the Oval Office, not the desk of underlings like Watt, "who will go down in history as one of those Cabinet officers who most seriously betrayed the public trust," hiding behind his own "caricature." Target unsympathetic congressmen in the fall elections, he urged them. "If some political heads must roll, so be it."

It was a call to arms by Carter, honored at the cocktail party by the Wilderness Society's annual Ansel Adams Conservation Award, citing his efforts to set aside 100 million acres of federal lands in Alaska as wilderness. Grateful outdoorsmen (and women) applauded, burying their hatchet with Carter.

"He really socked it to Reagan," beamed Bill Turnage, executive director of the Wilderness Society.

But a few had complaints about Carter's record. "We were constantly battling his administration," recalled Lewis Regenstein, vice president of Fund for Animals, a Washington, D.C.-based wildlife lobbying group. "He took pro-industry, anti-environmental stands on things like synfuels. Environmental regulations had to be made cost effective. Reagan didn't start that. But Carter looks great now that we've got these radical corporate socialists in power."

As Carter moved through the crowd to greet friends, he declined to elaborate on comments he made earlier in perhaps his most outspoken day since leaving the White House that Israeli officials had told him they were given "the green light" by the Reagan administration to attack Lebanon. His account was later termed "incorrect" by Secretary of State George P. Shultz.

But his feisty words on the environment reminded Claude Terry, 45, a lean outdoor guide, of the former Georgia governor who once insisted on shooting the most dangerous rapids on the Chattooga River with him. Lester Maddox, the clownish Georgia politician, was lieutenant governor at the time.

"Carter insisted on going down the rapids," said Terry, shaking his head. "I wasn't worried about him, just what the people of Georgia would do to me if I made Lester Maddox governor."