WASHINGTON — The debate over whether Congress should force universities to spend at least 5% of their endowments each year is about to heat up.

Today Senator Grassley, a Republican of Iowa, and Rep. Peter Welch, a Democrat of Vermont, are scheduled to host several university officials for a panel discussion on how universities should be spending their endowments. Both have argued that universities should be spending more of their endowment money, which is not taxed, to reduce tuition costs.

More than 135 colleges have reported endowments of more than $500 million, according to figures that Mr. Grassley has cited. Harvard University’s endowment, which led the pack, was last gauged at $34.9 billion.

In recent opinion pieces, Mr. Grassley has floated the idea of mandating that universities spend 5% of their endowments each year.

An aide to the senator said the event today could “lead to specific legislation.”

In February, Mr. Welch, whose late wife was a dean at the University of Vermont, introduced legislation requiring that at least 5% of an endowment be spent annually on reducing tuition and other student costs. Expenditures on new buildings, faculty hires, or research facilities would not have counted toward that 5%, meaning such legislation would have necessitated expenditures far in excess of 5%.

The congressman withdrew the proposal shortly thereafter, but said last week in an interview that he is considering new legislation. “I touched a nerve,” Mr. Welch said. “I was quite amazed at the resistance on the part of the higher education community.”

At a time when Columbia University and New York University both charge more than $50,000 for a year of undergraduate education, including room and board, legislation to force universities to subsidize those costs further has a chance at gaining traction, education policy analysts say.

“Endowments are red meat,” an education analyst at the Cato Institute, Neal McCluskey, said. “Intuitively it has an appeal to the public: that these schools aren’t paying their share and getting special breaks.”

Mr. Welch argues that the endowments of universities should be regulated like those of private foundations, which generally are required to spend 5% of their investment assets each year.

“I don’t see why they should be exempt from the same 5% rule that applies to the Ford and Gates foundations,” he said of universities.

Spending requirements intended for private foundations, whose stated purpose is to provide funding, are not necessarily a good fit for educational institutions, university officials and their trade organizations say.

“There is real concern that if you try to propose that kind of requirement, you’re going to have a long-term impact on the institutions that play an incredibly important role in our society,” a spokesman for the Association of American Universities, Barry Toiv, said. “You’re going to potentially damage a system that provides private philanthropic support for education and research in this country.”

Universities also are expressing concern that the debate over endowment expenditures is too focused on tuition costs. When Mr. Grassley and Senator Baucus of Montana, both Senate Finance Committee members, sent out a questionnaire earlier this year seeking information on how endowments are spent, Princeton University’s response noted that “very few of the questions” dealt with research programs.

“The endowment makes very substantial contributions to the operating and capital costs of the cutting-edge research that fuels America’s competitiveness, at a time when federal and other sources of support are failing to keep pace with rising costs,” Princeton’s president, Shirley Tilghman, wrote in the university’s response.

Ms. Tilghman, who is also on the executive committee of the Association of American Universities, is scheduled to speak at today’s event on a panel called “Are Mandatory Payouts Beneficial?” In addition, the president of Amherst College, Anthony Marx, and two others are scheduled to speak on the panel.

While not an official Senate hearing, the event will take place in the finance committee’s hearing room.

As it stands, universities on average spent 4.6% of their endowments in 2007, according to a study of 785 institutions of higher learning in American and Canada by the National Association of College and University Business Officers.

Last year, Harvard spent 4.6% of its endowment, according to a letter by its president, Drew Gilpin Faust, to Messrs. Grassley and Baucus. Ms. Faust says the university “targets a payout rate of approximately 5%,” although, according to Ms. Faust’s figures, it has hit that only once in the last decade.