Thousands of college students and parents are clogging phone lines and rushing to Internet sites in a scramble to refinance college loans before a sharp interest rate increase this weekend.

An almost 2 percentage point interest rate increase for federal student loans kicks in Saturday, and advisers say that not refinancing could cost thousands of additional dollars in interest in the decades after a student enters the work force.

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At the Missouri Higher Education Loan Authority, the nation's 12th largest student loan holder, calls are coming in at a clip of up to 15 a second, contributing to a tenfold increase in applications for student loan consolidations, said Raymond Bayer Jr., the agency's interim executive director. Other loan agencies also are experiencing high demand.

For-profit Sallie Mae, the nation's largest student loan holder, is on pace to meet or exceed last year's late crush of student loan consolidations, said Pat Scherschel, the company's vice president for loan consolidation.

"There are very few situations in which it is not advisable for a student who has outstanding loans to consolidate, because they will lock in" relatively low interest rates, said Sandy Baum, an economics professor at Skidmore College in Saratoga Springs, N.Y. Baum is also a financial aid analyst for the College Board education association that produces the SAT college entrance exam.

The Indiana Secondary Market for Education Loans began emphasizing consolidation loans last year and already has seen an 83 percent increase in applications this year, said Bob Zier, vice president for loan consolidation.

Nonprofit student loan agencies in states including Iowa, Ohio and Texas also have seen sizable increases in their applications as the rate increase approaches, said Alexa Marrero, spokeswoman for the Education Finance Council, an association of nonprofit secondary student loan marketers.

The federal government adjusts interest rates on its student loans each July 1 based on a formula tied to the yield on short-term Treasury bills.

The variable rate on a common Stafford loan dipped to as low as 2.77 percent for students in the 2004-2005 school year and 3.37 percent for graduates already making repayments. Those rates rose last year to 4.7 percent for students and 5.3 percent for graduates.

On Saturday, the rates will shoot up to 6.54 percent for students and 7.14 percent for graduates. Although the specific rates are different, they are rising by a similar margin for parents who take out loans to pay for their children's education.

Students and parents can lock in rates near the current levels by refinancing before Saturday. Because of a federal law that took effect June 15, they no longer must turn first to their incumbent loan holder to refinance if all their debt is held by the same source.

Before last year's interest rate increase, Sallie Mae received 367,000 applications for consolidation loans in June alone and more than 42,000 on the final day — a monthly total equal to some previous annual figures and a daily total equal to a month of applications, said Scherschel, the company's vice president for loan consolidation.

The Missouri Higher Education Loan Authority typically receives 150-200 consolidation loan applications a day. But on Monday, the agency received about 2,000 applications; on Sunday, it received about 2,300 — most over the Internet, said Bayer Jr., the agency's interim executive director.

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