Herbert E. Harris II fidgeted on his metal folding chair in Fairfax County's Fire Station No. 8 yesterday as 100 members of the Annandale chapter of the National Association of Retired Federal Employees meandered through their monthly agenda.

Harris, a former Democratic congressman seeking to regain his Northern Virginia seat, listened to an accounting of the chapter's membership rolls (net loss in August: 7), a debate about whether to computerize the group's mailing list (cost per member: 90 cents) and a reproach from the outgoing president that no one had brought cookies to the meeting.

Harris stood and sat and stood again and, when his turn finally came, launched eagerly into the gospel of the middle class, which he plans to make as the theme of his fall campaign. He portrayed himself yesterday not as the fiery liberal who has run against the oil companies, but as the defender of "fundamental American values" like home ownership and economic security.

"I think a society's greatness is measured by how it values its middle-income people's contribution to society," Harris told his audience. "I doubt there's very many of us in this room who didn't have some sleepless nights thinking about that home payment or that tuition payment. People who turn around now and call us 'freeloaders' make me mad."

While Harris spoke, his opponent, Republican Rep. Stanford E. Parris -- who had also been invited to the firehouse -- was recording radio and television commercials, according to a spokesman. Unlike Harris, the Republican has raised enough money to pay for extensive broadcast time, leaving Harris with the prospect of many more firehouse meetings to overcome Parris' acknowledged lead in recent polls.

Harris and Parris, whose names rhyme but whose personalities clash in almost every conceivable way, have each turned the other out of office once.

Parris won by fewer than 1,100 votes out of 190,000 cast in the 1980 Reagan landslide, and Harris hopes that disaffection with Reagan's economic policies will help reverse that margin on Nov. 2.

Harris told his Annandale audience yesterday that Reagan's economic policies have soured the suburban dream by making everyone economically insecure. High interest rates in particular, he said, are robbing the middle class by preventing most home sales and erasing the "fundamental American values . . . the right to own and acquire your own property, to build up equity in your own house.

"A lot of us who moved out to this area and raised our kids, got our grass cut -- about the only wealth we were able to put together was the equity in our homes," Harris said. "Now I think they're picking our pockets."

Harris made a special pitch for the government retirees' votes yesterday -- more than 15,000 live in the district -- saying Parris had threatened the benefits they earned through years of hard work. A recent survey by the National Association of Retired Federal Employees showed that most members who voted for Reagan in 1980 would not do so now, and some in the Annandale audience said they would not support Parris either.

A Parris spokesman said yesterday that Harris will not succeed in portraying himself as the champion of the middle class. "The majority of the people reject the type of liberal claims that he has supported over the years," the spokesman said. "So what he's trying to do now is change his spots. Well, that's okay, except he's got a six-year voting record."

Parris, who enthusiastically supported Reaganomics in 1981, has abandoned the president on some key votes this year, particularly concerning federal workers and retirees.