The Pennsylvania Higher Education Assistance Agency, one of the nation’s largest student loan operations, announced Wednesday that it would suspend making federal-guaranteed loans starting early next month.

The move offered further evidence of how the tight credit markets are affecting the industry, with some lenders warning that it could be more difficult and more costly for many students to obtain college loans for the 2008-9 academic year.

“Widespread lack of confidence in the capital market has spilled over into other asset classes, driving up our cost of borrowing and denying us the capital needed to fund new student loans,” said James Preston, the interim chief executive of the Pennsylvania lender, a state-owned company that both makes and guarantees loans.

Such loan operations have been dealing with two problems. Congress reduced subsidies to lenders in the federal-guaranteed student loan program. In addition, investors have recently shied away from purchasing securities backed by student loans, making it more costly for the lenders to raise the capital they need.