Sen. Robert T. Stafford (R-Vt.) is telling his constituents that his seniority in Congress means power and prestige for his state and vast influence on the issues of environment, education and arms control that they care about.

His main challenger says that same seniority has been converted into a pursuit of junkets, honorariums and personal perks that symbolize everything that is wrong with Congress.

The classic incumbent-vs.-anti-incumbent strategies being used here make the Sept. 14 Republican Senate primary perhaps the best early test of whether 1982 is going to be a high-turnover year for Congress.

After many years of relative stability, the membership of the House and the Senate started churning in the 1970s, as waves of public disillusionment swept Republicans or Democrats out of Congress. In 1978, only 17 of the 33 senators whose terms expired were returned; in 1980, it was 16 of 34.

So far, the 1980 primaries have not been too tough on incumbents. A handful of House members have fallen victim to redistricting or challenges, but only one senator, California's S.I. Hayakawa (R), has been forced to give up his bid for renomination involuntarily.

But many political observers still think the conditions may be ripe for a throw-the-rascals-out campaign, not only because of economic distress in several parts of the country, but because of the stories about scandals and boondoggles in Congress, ranging from Abscam payoffs to special tax breaks to the aborted plan for a third Senate gym.

Stafford is personally untarred by any of these publicized incidents, but he worries that he could fall victim to the anti-incumbent tactics of his two challengers, 1980 GOP Senate nominee Stewart M. Ledbetter and former Reagan White House aide John McClaughry.

"In all the years I've been in public office," Stafford said last week, "I've never seen so blatant an attempt to try to capitalize on general dissatisfaction with an institution Congress or incumbency."

Stafford said his polls show "I have a comfortable lead, but not the overwhelming margin I had a couple of months ago," indicating that the negative campaigning has had an effect. Other Republicans say they understand his margin over Ledbetter is between 10 and 20 points in the most recent polls, but described the situation as volatile. McClaughry is believed to be a distant third.

On the face of it, Stafford, 69, should be about as secure as a politician can be. He has been winning elections with regularity in Vermont since 1946, and has served the state as attorney general, lieutenant governor, governor, U.S. representative and, since 1971, senator. His last serious primary was 22 years ago.

With the GOP takeover of the Senate, Stafford became chairman of both the Environment and Public Works Committee and of the education subcommittee, giving the state its first power positions in the Senate in a generation.

He has built a careful, independent record. He supported the major Reagan administration economic measures, but pleased the state's large environmental, education and disarmament constituencies by his championship of the Clean Air Act, education for the handicapped, student loan programs and the nuclear freeze initiative, all in opposition to the administration.

But there is a reverse side of this seniority coin. Even some Republican officials supporting Stafford say that over the years, he has become more visible in Washington than in Vermont. He forced other ambitious officeholders to defer their hopes when he changed his announced retirement plans upon becoming a committee chairman. The logjam for 1982 got worse when Gov. Richard A. Snelling (R) changed his mind about retiring and decided to seek an unprecedented fourth term.

Ledbetter felt particularly victimized. Having come within 1.4 percent of defeating Sen. Patrick J. Leahy (D) in 1980, he thought he would have a clear shot at the nomination for the state's lone House seat if Rep. James M. Jeffords (R) had been able to move to the Senate in Stafford's place. "I think Bob Stafford should have retired," Ledbetter said. But since he did not, Ledbetter decided to force him out.

Ledbetter's tactic has been a negative radio and television campaign, hitting Stafford for collecting $25,000 in speaking honorariums in 1981, voting to raise the outside-earnings ceiling for senators, and supporting what Ledbetter calls "a behind-the-door pay increase" for lawmakers.

Most of all, he has hit at Stafford's chairmanship of the Interparliamentary Union delegation from Congress and what Ledbetter calculates to be "229 days of travel outside the United States in the last 11 years, causing him to miss 304 roll-call votes."

Stafford says the ads are "offensive, negative and in bad taste." And he challenges Ledbetter to say where he differs on substantive issues--a challenge Ledbetter is reluctant to take.

McClaughry, a domestic policy adviser to President Reagan and a self-described "Jeffersonian" conservative, has also criticized Stafford's travels. McClaughry has raised little money, however, so his charges are not filling the airwaves. Ledbetter, with the help of what he says will be more than $100,000" of his own and his family's money, is forcing Stafford to mount a major media campaign.

Money is one area where Stafford lacks the usual incumbent's advantage. At midsummer, he reported receipts of $146,407--more than twice Ledbetter's total at the time, and eight times McClaughry's. But it is vastly less than the $599,886 his GOP colleague, Sen. William V. Roth Jr., reported for his reelection campaign in the similarly small state of Delaware.

Stafford, as chairman of the Environment and Public Works Committee, has withstood heavy pressure from industry and the administration to weaken the Clean Air Act.

The Chamber of Commerce of the United States made revision of the act its top legislative priority this year, but despite its differences with Stafford, a Chamber spokesman asserts that the organization is neutral in the Vermont race. Stafford maintains "they have intervened, by suggesting to the industry PACs political action committees that I not be supported." His disclosure form shows he has received more money from business than have either of his rivals--and, unlike them, he also has the support of union, education and environmental groups.

If he is defeated, it will not be so much for lack of cash as because of his incumbency. And that could signal problems for a lot of other folks this year.