You might assume that Harvard undergraduates already have the credentials to guarantee success during their forays into Washington politics as summer interns on Capitol Hill.

Not so, said 14-year Hill staff veteran Jeanie O'Neil.

"A lot of students, even here, have a hazy 'Poli-Sci 101' understanding of how government works. They need more if they're really going to make it under pressure," she told 30 students--attending a two-day seminar--who, like undergraduates throughout the country, have gotten favorable nods from representatives or senators and are bracing for three months inside Congress.

O'Neil, who is working on a master's degree in public policy at Harvard's Kennedy School of Government, delivered a stream of not-so-funny anecdotes about cocky interns biting the dust: the intern who miscoded the office computer and repeatedly sent out form letters reminding prominent "right-to-life" spokesmen of his boss' position in favor of abortion, or the intern who tried to get chummy with a congressman by asking after a wife who had died some years earlier.

She added: "Whether you like it or not, you're likely to become the office gofer. You may soon begin to think that you went out for some sort of track team, rather than the U.S. Congress."

Her listeners took notes on yellow legal pads. Knapsacks and football buttons ("Impale Yale"), seemed suddenly inappropriate because the mood stayed serious, at times downright threatening.

Nevertheless, ambitions were high, even lofty.

"Half of the people in the Government Department at Harvard think they'll eventually be in Congress," said sophomore Peter Gelfman, a volunteer in Walter Mondale's presidential campaign.

He said rather than "trying to influence laws getting passed," he'll "just be trying to get the guy Mondale elected."

Dale Curtis, chairman of an undergraduate committee established to assist Harvard's Washington interns, explained why he spent last summer working for Rep. Sam Stratton (D-N.Y.): "I'm interested in being elected to Congress someday, so I thought I'd see what it was like."

For the few and the brave, O'Neil said, the glory is there for the grabbing. "With the proper preparation you can go in with a leg up on other people and show your boss that you're the person to rely on. That's really the secret. For many students there's a moral issue in that they see something wrong with the way things are done, with back scratching and other common practices. There are a lot of things they have to learn."

She described the "lovely taste of athlete's foot in the mouth" enjoyed by overeager staffers who embarrass their bosses with poorly crafted research or naive questions asked in front of influential constituents.

"Interns do get fired," O'Neil said several times.

She reviewed Hill arts such as answering irate letters from constituents with soothing letters that combine the right balance of facts and ambiguity: "Even if there's nothing substantive to say, the minimum is stating to the voter that you see him as a reasonable human being who brought up a reasonable issue. It may be that's the best you can do."

If they have a slow day, the students were told to dream up statements their employers can add to the Congressional Record, honoring outstanding citizens back home--longtime Kiwanis-Club leaders, bake-off chairmen and the like. "Get to know your community, and then you can stick your neck out and make these kinds of suggestions," said O'Neil. "There's an opportunity for your congressman and an opportunity for you."

Given a shot at the big time--drafting bills or writing speeches--the interns-to-be were urged to act swiftly but cautiously. "You can't afford to make that crucial mistake, so know your limitations, as well as your strengths."

The students seemed undaunted. Curtis enthusiastically recalled his work with the House Armed Services Committee as a highlight of last summer--"actually going over the Defense Department authorizations and learning about the various weapons systems."

He also cast the mundane chores described in class in a far more positive light: "Getting the letter from the little old lady--maybe she's not getting her Social Security check or something--doing the research and making sure she gets what she needs: that's the meat and potatoes of government, I think. That seems a lot more real than a lot of other things going on."

Others echoed a similar desire to discover the "real" government behind the headlines and speeches.

Gelfman, who worked last year for a small liberal political-action committee, conceded that "there are a lot of boring things in the life of an intern . . . a lot of what you do depends on luck." He said a rough day at the office is fast forgotten when you can track down a few buddies and "kind of crash good receptions and that kind of thing."

The intern entertainment pipeline, not a central subject of the Harvard seminar, functions smoothly from June through September, according to those who have worked on the Hill. Any buffet table not under strict guard is vulnerable to roving packs of summer staffers.

"Generally you go to things with other interns," said Margaret Groarke, another student. "Even if it's a Saturday, people come in the uniform: the same clothes they go to work in, khakis and ties. It's pretty amusing."

Kenneth Burt, a graduate student at Harvard's Kennedy School who will work this summer for Rep. Robert T. Matsui (D-Calif.), emphasized: "The social life is very, very important to interns. It's not just to have fun but to network with other people who may eventually help your career. That's something that can last a lifetime."