Patricia A. O'Brien's room on the second floor of the Office of the Registrar is orderly and neat--her desk free of papers, everything in its place.

But her job is anything but orderly. O'Brien is one of three people in charge of assigning hundreds of courses to classrooms, a hectic role she compares to putting together a puzzle.

In the months before registration, some courses are slotted into classrooms controlled by individual departments, O'Brien says. But the rest, about 80 percent of all classes, must then be put into about 20 percent of all available rooms.

"It's like a matching game," O'Brien says. "We think of all the factors involved" and try to make "the puzzle fit together," she adds.

O'Brien calls these factors "inventory." They include the room preference of the professor, the expected enrollment and whether audio/visual equipment is necessary.

Requests can be difficult to accommodate because many professors want the same rooms at the same time. O'Brien says this problem sometimes complicates her job.

"[But] professors understand the constraints," O'Brien says. "Usually [it's] something that can be negotiated."

For an office that is in "constant communication" with faculty and administrators, there is little personal interaction. Most contact occurs via e-mail and telephone.

Along with negotiation comes a lot of research. O'Brien and her two colleagues examine courses' past enrollment and location to determine room assignments.

Much of the work for the fall semester begins in May when FAS' Courses of Instruction is sent to the printer. The office is operating on a deadline: the supplement that appears in the mailboxes of students must be ready to print in late August.

However, each semester, some Harvard classes get an unexpectedly large turnout. What happens when the students don't fit in the classroom?

Yesterday, students crowded Harvard Hall for Government 1540: "The American Presidency," a popular government course taught by the Kennedy School's IBM Professor of Business and Government Roger B. Porter.

If the enrollment exceeds the room capacity, the course may need to be lotteried, Porter says.

But O'Brien says meeting professors' needs is the first priority.

"If we didn't have a room, [we'd look] at a change in time," O'Brien says.

Porter says he understands the difficult position of administrators like O'Brien.

"I'm very sympathetic to the problem they face," he says.

In the past, Porter has faced similar situations, but adds that each time the issue was resolved.

"They [the registrar's office] have been good in trying to work within the constraints they have to accommodate," Porter says.

While the space issue with "American Presidency" has not been solved, Porter says, "I remain an optimist."

O'Brien and her two colleagues do more than assign classrooms. They are responsible for the publication of Courses of Instruction and the online course database, as well as scheduling section locations.

O'Brien says assigning sections poses a similar problem.

"It gets tough and tight, but we do the best we can," she says.

With all her mentions of puzzles and challenges, her job might seem full of bureaucratic headaches. But she says she loves her work.

"[It's] an interesting challenge to come in and not know what's going to happen," O'Brien says.