“How much do you need to save for future generations, and at what point are you gouging today’s generation?” said Lynne Munson, of the Center for College Affordability and Productivity in Washington.

In January, the Senate Finance Committee requested detailed endowment and spending data from 136 colleges and universities with endowments of at least $500 million, with a possible eye to forcing them to spend at least 5 percent of their assets each year, as foundations are required to do. Large, tax-free endowments “should mean affordable education for more students, not just a security blanket for colleges,” said Senator Charles E. Grassley, Republican of Iowa, who is reviewing the data.

The commissioner of the Internal Revenue Service’s tax-exempt section said this spring that he wanted his agency to be more aggressive in ensuring that universities made “appropriate use” of their endowments. And officials in Massachusetts are studying a proposal for a 2.5 percent tax on the part of university endowments greater than $1 billion  a threshold exceeded by nine of the state’s universities.

“The endowments have grown to such an astonishing extent that people are asking, if the wealth and the value of the tax exemption are increasing, is the public benefit increasing, as well?” said Evelyn Brody, a tax professor at Chicago-Kent College of Law.

This year, Ms. Brody said, the debate has entered new territory. Traditionally, discussion about endowments has focused on the balance between using the money for the current generation versus saving it for the benefit of future generations.

“Endowment spending has usually been a ‘when’ question, about when the money would be used for a charitable purpose,” she said. “But now, it’s also being viewed as a ‘what’ question. What is the money for? And I think that’s new.”