WASHINGTON – In May 1974, Rep. William S. Cohen, a Republican freshman on the House Judiciary Committee, was gathering evidence that led to his eventual vote to impeach President Richard M. Nixon.

But outside the Watergate hearings room, Cohen needed a French speaker to respond to all the partisan mail from his Franco-American constituents in Maine.

He was in luck. A French exchange student — a senior at the private Holton-Arms School in Bethesda, Md. — had just begun interning in his office that month.

The internship formed an important part of the teenager’s year in America and would ultimately furnish an only-in-Washington coincidence: The congressman-and-future senator and U.S. defense secretary was passing off scut work to the future head of the International Monetary Fund, Christine Lagarde.

“Everyone was writing to the congressman, saying, ‘Impeach Nixon.’ ‘Don’t impeach Nixon.’ So I was introduced to the art of dealing with constituent members,” Lagarde, 55, recalls with a laugh. “During that year, at Holton-Arms, with my host family and interning in Washington, I learned more, and it mattered more to me, probably, than any year of my life.”

To most Americans, Lagarde might be an unfamiliar face that burst into the news as the successor to Dominique Strauss-Kahn, the former IMF managing director charged with the attempted rape of a New York hotel maid. To politicians and economists, Lagarde is the former French finance minister, who, as the new IMF chief, is overseeing the financial bailouts of three Western European countries.

But to a group of women from the Holton-Arms Class of 1974 and to the family that hosted her here, Lagarde was Christine Lallouette. She was the girl who already had graduated from a high school in France but had chosen to spend a year at Holton-Arms as an American Field Service exchange student. She was the girl who liked putting chamomile in her shampoo to make her hair more blond.

She smoked. She was a bit daring.

And she was the chosen confidante of a small clique of girls who didn’t mesh well with the preppier scene. Even today, they recall her impact on their lives as the slightly older, more worldly friend who managed to look fashionable even in the school’s requisite plaid skirt. For them, Lagarde’s appointment summons a time of life that often shapes personalities and is somehow never left behind. It was that way for Christine Lagarde, too.

INDEPENDENT STREAK

To her host family’s house in Bethesda, she brought a habit of European independence. She left behind her family in northern France, where her father, an English college professor, had just died, and she entered a more controlled American world, joining the family of Bill Atkins, an executive with the Touche Ross & Co. consulting firm, and his wife, Marion Guion Atkins, an accountant.

In the Atkins home, Lagarde was allowed to smoke only in her bedroom. She missed having a plentiful supply of yogurt. She hated the local tap water so much that she sometimes violated the family’s one-soda-per-day rule. She bristled at the before-midnight curfews.

“I came from the French high school system,” Lagarde says. “I used to be extremely independent when I was in France, but when I arrived in the U.S., it was much about, ‘Who are you going out with? What are you doing?’ I may have resented that.”

Lagarde and her host father forged a connection that, although neither knew it at the time, would endure deep into her professional life.

AMONG THE OUTSIDERS

At the beginning of her senior year in 1973, Page 4 of the Scribbler, the Holton-Arms student newspaper, carried the big news: “Holton Welcomes Christine Lallouette.” In a brief interview, the French newcomer expressed surprise that American women were not all “really fat and awful” and instead found them weight-conscious to “an obsession.”

At the end, the article perfunctorily noted her career ambition: “Christine eventually hopes to be a cultural diplomat for France, and plans to study political science when she returns next year.”

Within the social stratosphere of Holton-Arms, where President Gerald R. Ford’s daughter, Susan Ford, was also a student, Lagarde hung out mostly with a small band of outsiders, among them: Maggie Quiroga Mainor, the Argentine daughter of an international relations executive, and the late Gabrielle “Gabby” Geaslin Swartz, the daughter of a purported CIA operative.

Still, Lagarde never felt that she or her group quite fit in with her well-heeled and more traditional classmates.

In spring 1974, Lagarde graduated from Holton-Arms, wearing the school ceremony’s customary long white dress. Even as she climbed corporate and political hierarchies — becoming a lawyer and chairman of Baker & McKenzie, one of the world’s largest law firms, and then becoming the French finance minister — she never stopped relying on her host family.

“Whenever I’ve had to make a tough decision, I always got back to (Bill Atkins) and asked, ‘What is your view?’ ” she says. “He was a partner at Touche Ross, and he knew how partnerships at firms worked. He was a surrogate father in a way.”

COHEN REMEMBERS

William Cohen still remembers the intern who read and responded to his constituents’ letters in French, although he hasn’t talked with Lagarde since the internship. Now that he runs a global consultancy in Washington and she’s the IMF head and lives in Georgetown, he wonders whether they might rendezvous.

“Since she’s on the world scene in such a prominent position, I am sure I’ll make every effort to reach back out to her,” he says. “I’ve had outstanding interns in Washington, and I would count her as one of them.”

A very Washington thing to say, of course. And a lesson for those in high places: Always treat your interns well.