The adviser described Mrs. Clinton as flattered by President-elect Barack Obama’s interest but said she was agonizing over the decision. Mrs. Clinton likes being her own boss and is reluctant to give up the independence that comes with that, said the adviser, who spoke on condition of anonymity because the process was at a delicate stage.

“If you are secretary of state you work for the president,” the adviser said in an e-mail response to questions from The New York Times. “If you are a senator, you work for yourself and the people that elected you.”