That didn't look like a problem, since revenue and donations also have been rising. But in recent months, like homeowners stuck in a variable-rate mortgage, some schools have seen their debt payments surge, thanks to the collapse of a complicated line of dominos that includes bond insurers and banks. Instead of holding long-term debt at lower interest rates, they have gotten stuck with short-term obligations at higher rates -- a scenario they knew existed on paper but never expected to happen.

Others have become collateral damage from the collapse of Wall Street firms. Simmons College in Boston was placed on a watch list for a ratings downgrade because of an estimated $10 million exposure in a complex interest rate swap deal with now-bankrupt Lehman Brothers.

The financial crisis is "clearly very serious," said Paul Corts, president of the Council for Christian Colleges -- Universities. "I think people are sensing that this is not short-term. It's something that's going to take a couple of years to play out."

Enrollment at the 102 CCCU campuses grew 71 percent between 1990 and 2004, and Corts says he has no reason to believe member schools will close. But, "then again nobody knows what the ultimate extent of this whole financial crisis is going to be," he said.

Another potentially vulnerable group is historically black colleges, which, like Christian schools, have a limited recruiting pool. Some such institutions, like Morehouse and Spelman, have healthy endowments.

But others are more fragile, especially those with low graduation rates. Banks are tightening up credit standards, and increasingly denying students at schools where students are too likely to drop out. The Journal of Blacks in Higher Education has reported that there are 23 historically black colleges where more than two-thirds of entering black students fail to earn a diploma.

At St. Paul's College in Lawrenceville, Va., the graduation rate fell from about one-third to under 10 percent between 2002 and 2006, according to federal numbers collected by the group The Education Trust. President Robert Satcher said that number is higher now, but acknowledged the school faces serious financial challenges. It needs to add at least another 200 students to reach its goal of 1,000, and somehow despite the downturn must raise money to boost its tiny $4.5 million endowment.