As the nation’s credit crisis spreads through the financial industry like a wicked virus, it is affecting the ability of college-bound students to find enough money to pay for school.

Lehman Brothers, one of Wall Street’s most venerable investment banks before it sought Chapter 11 bankruptcy protection this week, had grabbed a slice of the $18 billion private student loan market in 2006 when it acquired CampusDoor, a student lender based in Carlisle, Pa., about 18 miles outside Harrisburg. But CampusDoor closed on the eve of Lehman’s collapse, becoming another in a string of private student lenders to exit the business.

More than 70 companies have stopped lending money to students since the start of the year. Bank of America is among them. In addition, Massachusetts-based First Marblehead, one of the giants, has drastically scaled back its lending.

The shrinking industry means one less source of money for American families to tap into to help pay for a college education. The impact of one closing, such as CampusDoor, is difficult to measure precisely, but financial aid experts said lots of students could be left in the lurch, without the money they had anticipated receiving.

It’s another sign of how the damage begun by the collapse of the subprime mortgage market is seeping into the everyday life of consumers.

“There may be hundreds of thousands of students who might be waiting, whose loans were approved but not disbursed,” Mark Kantrowitz, publisher of FinAid.org, said of CampusDoor’s closing. “They may or may not get those loans funded.”

“If you’re a borrower with a pending application, I wouldn’t count on getting that loan. If you’re a borrower who already has a loan, the worst-case scenario is you might have a different loan servicer,” added Kantrowitz, whose website offers financial-aid information and advice.

A woman who answered the telephone at CampusDoor referred calls to Lehman Brothers in New York City. Lehman did not respond to a request for information about its student-lending business.

As college tuition costs soared during the past five years, students and their parents began turning more often to private student loans to help bridge the gap between the amount they could raise – including student aid and what the federal government allowed them to borrow – and the actual costs of an education.

The private student loans were heavily marketed, and it wasn’t long before they became a huge business.

Sallie Mae, which severed its ties to the federal government in 2004, became a giant in the private student lending business. The company generated $7.4 billion in loan originations in 2006 and saw its business increase nearly 7 percent in 2007, when its loan originations amounted to $7.9 billion, according to information Sallie Mae distributed in June during a conference in New York City.

No surprise that Lehman Brothers – and other banks – would be attracted to the business. In 2006, Lehman quietly acquired fast-growing CampusDoor.

The nation’s credit crisis changed everything. Student loan companies typically raise money by packaging the loans into securities that are then sold to investors – the same way mortgages are sold. When the subprime mortgage crisis began roiling the markets, investors shied away from asset-based securities, and lending tightened up.

Even before homeowners began defaulting on subprime mortgages, CampusDoor and similar organizations were coming under fire for lending practices like those that led to the subprime fiasco.

Barmark Nassirian, associate executive director of the American Association of Collegiate Registrars and Admissions Officers, said the explosion of private loan programs was troubling. In many cases, he said, the private lenders were betting on students and schools that had high default rates.

“They were not federally regulated. They tended to have harsh conditions,” Nassirian said of the lenders. “This was no different than the subprime mortgage mess.”

While loans are still available, especially through the federal government, many financial-aid experts say prospective students will face tougher standards from lenders and will have to pay more for the money they borrow.

“It’s very difficult for students to get loans these days. This is what’s been happening over the past 12 months, and there hasn’t been much done to fix it,” said Keith Alliotts, chief executive of TuitionBids.com, a website that matches student borrowers with lenders. “Credit needs to be loosened up or there’s going to be a percentage of kids who can’t go to school.”