The demand for four-year college degrees is softening, the result of a perfect storm of economic and demographic forces that is sapping pricing power at a growing number of U.S. colleges and universities, according to a new survey by Moody's Investors Service.

Facing stagnant family income, shaky job prospects for graduates and a smaller pool of high-school graduates, more schools are reining in tuition increases and giving out larger scholarships to attract students, Moody's concluded in a report set to be released Thursday.

But the strategy is eating into net tuition revenue, which is the revenue that colleges collect from tuition minus scholarships and other aid. College officials said they need to increase net tuition revenue to keep up with rising expenses that include faculty benefits and salaries. But one-third of the 292 schools that responded to Moody's survey anticipate that net revenue will climb in the current fiscal year by less than inflation.

For the fiscal year, which for most schools ends this June, 18% of 165 private universities and 15% of 127 public universities project a decline in net tuition revenue. That is a sharp rise from the estimated declines among 10% of the 152 private schools and 4% of the 105 public schools in fiscal 2012.

The financial pressures signal that many schools are starting to capitulate to complaints that college has become unaffordable to many American families, observers say. At least two dozen private colleges froze tuition this fall, roughly double the previous year's total.