Anthony Norton, a junior at the University of Massachusetts in Boston, just learned a tough lesson in economics:

The credit market crisis is spreading to student loans.

Norton thought he was set when he deposited a $16,000 student-loan check to pay for summer classes and the fall semester. But when he started to pay bills for classes, rent, and other expenses last week, his checks bounced.

He was one of 500 students left in the lurch with the April 7 bankruptcy filing of The Education Resources Institute Inc., a Boston nonprofit that guarantees student loans. And his ordeal is only the latest example of chaos in the college loan market. More than 50 firms have abandoned or cut back their federal or private student loan programs this year, unable to raise money in the financial markets. Yesterday, Citigroup, one of the largest private lenders, said it would stop lending at some schools and end its federal loan consolidations.

While families used to secure student loans almost regardless of their credit history, "Those days are over," said Tony Erwin, director of financial aid services at Northeastern University in Boston and president of the Massachusetts Association of Student Financial Aid Administrators.

As students and parents begin the process of applying for financial aid and loans for the upcoming school year, Erwin warned, loans are going to be harder to come by and more expensive: "It's going to be a problem. There's no question about it."

Student loans have been among the easiest and cheapest loans to get - allowing millions of Americans to go to college as long as they promised to pay the bills after graduation. Given this year's challenging environment, many colleges are offering more assistance to students, such as more generous grants and direct government-backed loans with capped interest rates, such as Stafford loans.

But many families, especially those paying for private schools, will find that's not enough. For example, if a private college costs about $45,000 a year, a typical family will have to come up with at least $20,000 on their own, whether from loans or savings.

One Raynham mother and human resources executive was so concerned about nailing down private loans for her two sons in college that she applied in March, earlier than usual.

With $60,000 in tuition bills due this fall and her husband struggling with cancer, Lynne Tartaglia applied for $33,000 in loans from Massachusetts Educational Financing Authority, or MEFA. She received her approval on March 7.

Still, Tartaglia was nervous. So, loan agreement in hand, she contacted MEFA again. An e-mail she received in response said that Tartaglia had applied too early and that the rates and terms she was promised were not valid for the coming year. But she hopes they will honor her signed document.