On the Virginia side of the Potomac, one of the Washington area's premier political reform movements is faltering, a victim of the national drift to the right.

For the first time in 25 years, Arlingtonians for a Better County, the nonpartisan coalition founded by federal bureaucrats who wanted to fight Virginia's conservative, segregationist policies, is not playing a major role in the county's fall elections.

Sensing that the county's voters may have tired of the organization's liberal, "do-gooder" image, Arlington Democrats have taken charge of the race for the county board's only open seat -- an action that could mark the beginning of the end for the once-powerful ABC.

The organization grew dominant over the years by absorbing the political frustrations of federal workers, barred by the Hatch Act from participating in Democratic and Republican politics. In its salad days the independent ABC controlled every elected office in the county and was instrumental in driving conservative Rep. Joel T. Broyhill, one of the area's most influential congressmen, from office. But this fall, some of ABC's most influential leaders are, as two-time president Allen Kitchens unhappily puts it, "sitting it out."

The result has been to focus increased attention on the campaign of John Milliken, a 35-year-old Washington lawyer and a former congressional aide, who is running for the county board as a Democrat -- not as somebody who was the ABC candidate first and foremost and only happened to be endorsed by the Democratic Party.

Ironically, a Democratic victory Nov. 4 over Milliken's opponent, Republican-backed independent Simone J. (Sim) Pace, could mean the end of the ABC, which until recently has dominated Arlington politics.

"It's all over this year for ABC if John wins," said Kitchens, who fought the Democratic Party activists who wrested the key role in the campaign from the ABC at a bitter meeting last spring. Others agree and say that ABC's decline began five years ago when voters began opting for more conservative candidates, a change that Republicans say reflects the changing character of Arlington's population, as well as national trends.

Some ABC supporters say the party also has had difficulty getting its message across to voters who are more troubled by pocketbook issues than philosophical ones. "ABC has stood for big budgets and high taxes -- even though that wasn't true -- and the Republicans were very successful in conveying that image," said Arlington Sheriff Jim Gondles, a Democrat who was elected last fall."I had people who came up to me and said I'll vote for you but I won't vote for those ABC candidates."

The apex of ABC's power may have been 1974 when the Abc precinct organization provided Joseph L. Fisher with the nucleus of workers needed to defeat 11-term Republican Broyhill. But beginning in 1975 with the election of Dorothy T. Grotos and Walter I. Frankland Jr., the current chairman of the five-member board, Republicans have made steady gains in Arlington, despite its reputation as Virginia's most liberal jurisdiction. The GOP's gains there have come as the party has also registered gains in winning local offices in Fairfax County, Alexandria, and the rest of Virginia, the only southern state Jimmy Carter failed to carry in 1976.

Carter's popularity was high last spring when the Democratic Party assumed control of the Milliken campaign, pledging to elect a Democratic ticket "from the White House to the courthouse." Now there is widespread uncertainty about whether Carter will help or hurt Milliken.

Another unknown is the effect Milliken's former boss and political mentor, Rep. Fisher, will have on the election. Fisher, who is running for a third term this fall, and Milliken, his former executive assistant, are running as a team.

Some veteran politicians say that ABC is already dead, a victim of a conservative backlash against increasing property taxes and what was perceived as the coalition's liberal policies. Board member Frankland refers publicly to ABC as "Arlingtonians for a Bankrupt County" and some veteran Democrats concede that the nickname may have stuck with the voters.

A few years ago that would have been unthinkable. As recently as 1975, ABC controlled every seat on the County Board and school board. It was the spawning ground for a generation of political leaders, including Fisher, who repeatedly won elections by running on a platform consisting of a triad of issues: good (and integrated) schools, limited growth and good services like parks and libraries. ABC was formed in 1955 by a handful of federal employes who wanted to fight the Byrd political machine that then controlled Virginia and had insisted on "massive resistance" to school integration.

"ABC is like the elite in a small town . . . where people go to the same parties, manage each other's campaigns and appoint each other to various committees," said one prominent ABC member several years ago. Frankland's frequent public attacks on ABC as "that little clique which for years has run county government the way it wanted" probably did not help ABC's image.

Most say ABC's most serious problems date from 1978 when the Republicans successfully copied ABC's precinct organization. Others say that Arlington's transient population -- a sizeable portion of which has never heard of ABC's early accomplishments -- hurt the group as did Arlington's transformation from a bedroom suburb peopled by young families with children to an urban county populated by large numbers of newly arrived ethnics, retired bureaucrats and affluent singles.

"We need to work on our image and on attracting new members," concedes ABC chairman Amy Appelbaum.

ABC has also been hurt, its leaders say, by a blurring of once sharp distinctions between the Republican-backed and Democratic-endorsed candidates. "The Republicans have become successful because they stopped behaving the way they used to and started running attractive candidates," said Cornelia Motheral, a longtime ABC activist. "They've picked up on a lot of our issues like housing and a reasonable approach to growth."

Tom Hall, a Labor Department hearing examiner and ABC leader, agreed. "I often find myself being more in line with the way Dorothy Grotos votes than with my own people," said Hall, who is limiting his role to attending candidates' nights and fund-raisers for Milliken, but cannot legally canvass or do precinct work.

"ABC does not have a monopoly on good organization or issues," said board member Grotos, whose party will control the county board until at least 1983. "By reading their literature you'd think they invented motherhood and everything."

"ABC stands for a certain approach to politics, more a long-range, thoughtful, creative approach to issues rather than a short-term, reactive thing like the Republicans," replied Marianne Karydes, a longtime member of the ABC and Democratic Party who recently became a federal employe.

"I think ABC has provided a shield for people who thought politics was beneath them but that civic issues were somehow sacred. Some people feel they're preserving their political chastity by supporting nonpartisan candidates," Karydes added. "There's an awful lot of football game pep-rally stuff about the Democrats."

Speculation about ABC's death may be premature, Karydes says. "What political movement doesn't have its surges and periods of decline? I don't think that this is any sort of death knell. If John [Milliken] wins and Carter loses what will that prove?"

"This is probably a bad year to draw conclusions," said State Del. Warren Stambaugh, who said he is not willing to declare ABC moribund. "There's no reason ABC can't go back to being an issue organization which holds public forums."

Kitchens, a former two-term ABC chairman, does not see it that way. "I never felt we did any good at all with those issues forums," he said, his voice laced with disgust. "The whole purpose of ABC was to take control of the county government."