Sen. Robert T. Stafford (R-Vt.) has been in public office most of his adult life, and he had to reach far back to find an identification with his audience, members of the Vermont Farm Bureau.

As a youth, he recalled, he'd worked on a farm milking cows for $20 a week and had found it hard work. It made a man appreciate going to Washington where, he said, there isn't any heavy lifting to do.

Telling constituents his life is softer than theirs is the sort of after-dinner joke only safe politicians can use. But it's easy for Stafford, who, after a year in the Republican-controlled Senate, has emerged as a major beneficiary of being a Republican in 1981.

He has been elevated from the ranks of obscurity to committee and subcommittee chairmanships, attained a modest national prominence and become a man with whom the White House must contend.

Stepping out of the crowd in Washington has made Stafford's position at home almost impregnable. A year ago the word got around that he might not seek reelection in 1982, prompting two prominent Republicans to begin maneuvering to become his successor.

Stafford changed his mind, partly because he likes his new role of power-wielder, and the others politely bowed out. No Democrat is eager to take him on.

Republican dominance in the Senate this year raised Stafford to chairman of the Environment and Public Works Committee and chairman of the education subcommittee of the Labor and Human Resources Committee. He has, as head of the former, inherited the "Mr. Clean Air" title once held by another New Englander, Edmund S. Muskie of Maine.

He is in a position to defend both environmental and education programs from the Reagan administration's budget cuts and shifts to block grants. Both areas are vitally important in Vermont, which, despite its reputation as a citadel of rugged individualism, relies heavily on federal grants and ranks near the top among states in terms of getting back the tax money its citizens pay to Washington.

"His position of leadership gives him an image of influence and leadership in the nation," observes the state Senate's majority leader, Stuart Smith, a Buick dealer in Rutland. "Bob has kept a pretty low profile over the years and he's probably a little more liberal than a lot of Republicans here would like. But Vermonters will vote for someone of stability and influence."

Stafford also benefits from his strategy of keeping a certain distance from the administration.

This year's budget cuts are only beginning to appear on Vermont's horizon and the legislature will have to make some tough decisions next spring on filling the gap created by declining federal aid for food stamps, fuel assistance, medical care, education and other programs.

There is talk of doubling the state's low sales tax and Democrats are gleefully preparing to blame it on Republicans in Washington, including, if they can, Stafford.

Stafford has gone along with much of the Reagan program, voting with the president on the overall budget reduction and tax cut and, most recently, the sale of Airborne Warning and Control System planes to Saudi Arabia. His voting record this year, in general, is more solidly Republican than it was before his party controlled the Senate, and his reputation as a "gypsy moth"--a Republican who battles the president--is somewhat exaggerated.

But Stafford has resisted on occasion, stubbornly refusing to add his key committee vote to an administration plan that would have folded aid for the handicapped and special education programs into block grants. He also has served notice he will not accept the sweeping changes in the Clean Air Act that the administration has vaguely promised.

"I've always been a compromiser if I could do it," Stafford said during an interview in his Rutland office. He said he will offer some "fine-tuning" of the Clean Air Act, enough to reduce the more obnoxious red tape, but will not loosen the fundamental clean air standards that he and Muskie wrote.

In Washington, Stafford said he is besieged by representatives of the automobile and public utility industries begging for relief from costly overregulation, a complaint endorsed by Ronald Reagan during the 1980 campaign.

But "up here in Vermont," he said, "I don't hear anything about business being overregulated. The environment is a big issue up here. We've got a bottle law and we don't have ads on the federal highways. We've got strict real estate controls. Vermont strongly supports a clean environment."

Stafford said he would like to work out a compromise with the White House on reauthorizing the Clean Air Act, suggesting that it might save congressional Republicans a lot of sorrow next year.

"I hope the White House has read the latest Harris Poll like we have," he said, referring to a public opinion sample that underscored national support for clean-air legislation. To impair the act, he said, "would be to hand the Democrats a dandy issue next year."

Stafford, who also has served as state's attorney, deputy attorney general, attorney general, lieutenant governor, governor and U.S. congressman, has earned a reputation over 24 years as a pragmatist and compromiser who is usually positioned near the center of his constituencies. Soft-spoken and rarely angry, he is well-suited to a state that regards charismatic politicians and ideologues with suspicion. He can also be exceptionally stubborn on issues important to him and Vermonters.

"He's been a pretty solid Republican this year," said one Senate aide who has followed his career. "But he's always got a bottom line below which he won't go."

Vermont's Democrats concede the 68-year-old Republican is well placed for 1982, when they foresee a considerable revolt against Reagan economics and budget cuts.

Democratic state Sen. Robert V. Daniels of Burlington, the minority leader, said Stafford's distance from the White House over environmental issues has enabled him to avoid the taint of Reaganism.

"He's represented Vermont well on such things as abortion, women's rights, the environment," said Daniels. "He's liberal enough that Democrats have trouble staking out a place against him. He's well-positioned in the center of Vermont."