Two of the most powerful people in the museum world right now are not museum directors, or curators, or wealthy donors. They didn’t even major in art history. Still, Sarah James and Laurie Nash, two principals at the executive search firm Phillips Oppenheim, are playing a crucial role in two decisions that will shape the New York art world for years to come: the selection of the future directors of the Metropolitan Museum of Art and the Solomon R. Guggenheim Museum and Foundation.

Virtually all museum boards today, when faced with the task of replacing a director, hire a search firm. The firm will generally begin by interviewing people at all levels of the museum to get their feelings about what is needed in the new leader. After making sure the board’s search committee knows what it is looking for, the headhunters, drawing on their large network of connections and a good deal of additional research, will offer a list of names. They schedule the interviews, prep the candidates, and remind the board to stay focused on its criteria, in order to make the best possible match between a museum and a director.

There are only a handful of individuals and firms who are major players in the museum world. Malcolm MacKay, at Russell Reynolds Associates, has placed some of the most prominent directors, including James Cuno at the Art Institute of Chicago, Anne Poulet at the Frick Collection, and Lisa Phillips at the New Museum of Contemporary Art. Nancy Nichols, at the firm Heidrick & Struggles, was also at the top of the field, when she became ill and died in 2002 of Lou Gehrig’s disease.

Phillips Oppenheim, which was founded in 1976, is much smaller than these firms and works exclusively with not-for-profits. Before the Guggenheim hired Ms. James and Ms. Nash last summer — at that point, to conduct a search for a director of the New York museum, who would serve under the Guggenheim Foundation director, Thomas Krens — the highest profile search they had conducted was for the Indianapolis Museum of Art, where in 2006 they placed Maxwell Anderson, a former director of the Whitney Museum of American Art.

Now that they are running both the Met’s search and the Guggenheim’s — which became much bigger after the announcement last week that Mr. Krens would resign — Ms. James and Ms. Nash have gone from being relative underdogs to being at the head of the pack.

“I think the [Met’s] search committee was probably surprised to find themselves seeing the value of a small firm,” an individual in the museum world who asked not to be named said. The choice, he suggested, “speaks to the Met’s interest in turning a page and thinking freshly about their leadership challenge.”

Ms. James and Ms. Nash, who are both in their early 40s, were described by people who have worked with them as having complementary personalities, which enable them to connect with a wide range of people. (Ms. James and Ms. Nash declined to comment for this article. ) Ms. James, who is from California, attended the University of California at Berkeley, and served in the Peace Corps in Mauritania, is the effusive “front woman,” while Ms. Nash, who is from the East Coast, attended Yale, and coached sports at secondary schools, is more detailed and methodical.

“Sarah was more the high-profile personality type. Laurie was very concrete, very thorough,” a vice chairman of the board of the Parrish Art Museum, which worked with Phillips Oppenheim to find a new director, Susan Griffin, said. “They bounce off each other very well.”

People who have worked with them as job candidates described them as honest and supportive about the search process, and sincerely interested in finding the right fit for both parties.

“I felt like I was talking to somebody who genuinely cared about me, and was really working with me to envision my future,” the director designate at the Parrish, Terrie Sultan, said. “At the end of every conversation, [Laurie] would say, ‘What else do you need from me?'”

The director of arts at the Smithsonian Institution, Susan Talbott, whom the pair recently placed as the new director of the Wadsworth Atheneum in Hartford, Conn., said that Ms. James was very forthcoming “about the positives and the negatives of the institution. She wasn’t painting an unrealistic picture.” Ms. James also gave her helpful advice about how to present herself to the board, she said.

From the other side, trustees said that Ms. James and Ms. Nash forced them to spend a significant amount of time, before they saw any candidates or résumés, articulating what the institution needed in a director.

That discussion could be frustrating, one of the co-chairmen of the Wadsworth Atheneum search, Susan Rottner, acknowledged. “The committee would say, ‘Just give us the names.’ And they said: ‘We have names, but if you haven’t convinced yourselves of what are the key competencies you’re looking for, then it’s going to be hard to evaluate the people we bring to you.'”

The process of deciding what the institution needs will be critical for the Met’s board members, many of whom probably can’t imagine the museum without its director of 30 years, Philippe de Montebello. In the case of the Guggenheim, the museum-world insider who didn’t want to be named said it was probably the headhunters’ candid advice about the difficulty of finding someone for a no. 2 job that convinced the board to let Mr. Krens go.

“Most headhunters are always thinking about their next job, so they’re loath to come across to a normally very powerful and self-regarding group of trustees as telling them how the world should be,” the insider said. “Sarah in particular is very blunt about the competitive environment, the other searches that are going on, and the reservations candidates might have based on an institution’s past experience with directors.”

That straight-shooting style is reassuring to both trustees and candidates, he said. With many headhunters, he explained, “there’s a degree of calculation in each discussion, a kind of minuet. With Sarah you always feel like you’re getting the straight stuff.”