The place is an elementary school cafeteria in Fairfac County. The event is a debate between two long-time Northern Virginia politicians who want to be elected to Congress. The politician who is jumping up and down from a steel folding chair, making a racket, grabbing the microphone and shouting "Oh, my Lord" and "My goodness" is Democratic Rep. Herbert E. Harris II.

"They say I'm a fighter. Yes, I'm a fighter," says Harris, knitting his brows. "I've fought the vested interests and I just love doing it."

Herb Harris, who's been called a "preacher" by his Fairfax supporters, a master of "histronics" by a congressional staffer and a "blatant phony" by political opponents, now is fighting with Republican John F. Herrity (the other politician at the elementary school) to retain his seat in Congress.

The fight, Harris says, is going well. "I'm a fella who is very, very secure as to his product," Harris said in an interview. He also believes that he is a fine salesman of his product.

At the elementary school. Harris demonstrated his salesmanship.

"How did you vote on the proposed constitutional amendment for full representation in Congress from the District of Columbia?" asked 11-year-old Chris Bjorson, who'd come to the debate with his parents.

Before he got up from his folding chair and put his death-grip on the microphone, Harris whispered around and found out the boy's first name.

"Well, Chris," Harris replied, smiling warmly, "I believe in equal representation for everybody, no matter where they live."

Harris went on to say that he voted for the full-representation amendment and argued that anyone who doesn't believe in representation for all Americans is un-American. "I've got a funny notion that everyone deserves to have his or her voice heard," Harris said.

The audience applauded. Harris' opponent glowered. The congressman beamed.

Harris, 52, the son of a Kansas City Mo., wholesale jeweler, has been beaming in Northern Virginia since his first involvement in politics in 1956 a a chairman of the schools committee of the Federation of Civic Associations.

When Harris sat on the Board of Supervisors, he frequently sneered at and railed against the man he now must defeat to get back to Congress.

A graduate of Georgetown Law School who once worked as a registered lobbyist for the Australian Meat Board Harris served seven years as a Fairfax County supervisor from the Mount Vernon District before he was elected to Congress in 1974.

"Harris obnoxiously pushed things down Herrity's throat at every opportunity," according to a long-time Fairfax observer.

Herrity, a lone Republican on the board when Harris was a supervisor, now is chairman of the board. His bristling resentment against Harris has made the 8th District race the most acrimonious in the Washington area.

The election also is close, with most political observers in Northern Virginia saying it is too close to call. A few give Harris a slight edge.

The enmity shared by the two men has come bubbling up in almost all of the more than 20 debates and joint appearances they have made. Herrity, referring to his opponent's legal reasoning on a constitutional amendment banning federal aid for abortions (which Herrity favors and Harris doesn't), said in one debate he was "ashamed" that both had gone to Georgetown Law.

Harris, for his part, has not made personal verbal attacks on Herrity. He has, however, made his feelings quite clear by his facial expressions during their confrontations. When Herrity, for example, says it will be possible to pass a constitutional amendment requiring a balanced federal budget, Harris winces, rolls his eyes and shakes his head. The impression is that he thinks his opponent doesn't know what he's talking about.

"From the very beginning my opponent has tried to make this campaign into a personal dogfight. But this is not the way I campaign," Harris told a reporter. "Of course I do tend to make faces. My wife Nancy tells me "old rubber face." Apparently my face at times, does have certain expressions. This is not intentional."

Herrity has based his campaign on painting Harris as a big spender. The Republican points out that Harris voted for higher social security taxes, a $61 billion deficit for fiscal 1978 and for more House office space.

Harris is considered, along with Democratic Rep. Joseph L. Fisher of the neighboring 10th District, among the most liberal of Virginia's congressional representatives. Americans for Democratic Action, a nonprofit liberal lobbying group, rated Harris in 1977 as coming down on the liberal side of issues in 70 out of every 100 House votes.

In 1976, Republican challenger James R. Tate attempted to portray Harris a too liberal for the 8th District, which is made up of many retired military people and high-level governmental employes. Tate garnered just 43 percent of the vote to Harris' 51 percent.

"The people in my area are fed up to here (Harris signals with his hands to a point just above his eyes) with this liberal-conservative kind of shorthand. What they want to know is who is working on their problems and how successful is he."

Harris has based his campaign appeal on what he calls his "effectiveness." He justly claims credit for fighting for Metro funding as chairman of the House District subcommittee that deals with Metro money, for helping obtain a permit for Fairfax County to tap the Potomac River, for defeating a proposed commuter tax and for changing an 1883 law that set quotas on the number of government jobs available to Virginians.

"Harris is an aggressive and fairly imaginative congressman who is very attentive to the things that affect his constitutents," said a senior staff aide of the District Committee, one of the three on which Harris serves.

Although one member of Congress, who has had conflicts with Harris and who refused to be identified, calls the congressman "an irritating, overdramatic phony" several congressional staffers say that Harris is intelligent, works hard and rarely misses a committee meeting.

Even from those who praise Harris, however, comes a common complaint about the congressman's speaking style.

"Herb just looks like he is always posing. Even when I know he is being sincere, he looks like he's posing," said one Fairfax government official, who also refused to be identified.

Harris, aware of this criticism, says he cannot help but look excited when he talks about the things he's done in Congress.

"I'm not a man to politely applaud when the touchdown is scored," he says.