If you haven't consolidated your student loans yet to lock in record-low interest rates, you should become a quick study if you want to save thousands of dollars.

The lowest interest rates in 39 years have made college-loan repayment more manageable lately, especially for new graduates with little money to spare.

But that's about to change: Interest rates for federal Stafford and PLUS loans are reset each July 1 based on the rate for 91-day Treasury bills to be set at the U.S. Treasury's final May auction. And with T-bill rates rising all year, experts expect rates on Stafford loans to students and PLUS loans to parents to rise by roughly 2 percentage points to more than 5 percent on July 1.

Consolidate by June 30, and students who graduate in 2005 can lock in today's 2.875 consolidation rate for as long as 30 years.

That's slightly higher than the rock-bottom 2.77 percent Stafford loan rate for in-school students and those still in the six-month grace period after graduation. But that slightly higher rate is fixed for the life of the loan and saves more than $4,000 on the typical $20,000 Stafford loan repaid over 20 years, according to Sallie Mae, the largest source of U.S. education loans.

Automatically debit payments from your bank account and your interest rate is shaved another 0.25 percent. Pay on time for 36 months, and your interest rate is lowered an additional percentage point for a consolidation rate of 1.625 percent.

"That's less than inflation and far lower than interest rates for mortgages, car notes or credit cards, but be sure to do your homework first to get the best deal and make sure loan consolidation is for you," Sallie Mae spokeswoman Martha Holler advises.

If you're out of school and already repaying Stafford loans, consolidation of $20,000 in loans could save you $4,500 over 20 years if you consolidate before July 1. Your consolidation loan will carry a fixed interest rate that is the weighted average of the rates on the loans you consolidate, rounded up to the nearest eighth.

Parents repaying a $20,000 PLUS loan would see a similar savings. Unlike students, who do not start repaying loans while they're still in school, parents with PLUS loans can consolidate while their child is in college.

Besides interest savings and stretched-out payments, borrowers can prepay a consolidated loan at any time with no early payment penalty.

Need another reason to consolidate student loans now? President Bush and his congressional allies propose ending fixed-rate consolidation loans.

The president's 2006 budget proposes raising the limit on the amount of federal loans that students can borrow. But to cover that $2.6 billion cost, the administration would end fixed-rate consolidation loans and replace them with variable-rate loans that fluctuate with market rates but could rise no higher than 8.25 percent.

"Moving to variable interest rates on consolidation loans will create a single, equitable interest-rate formula for borrowers: That's just basic fairness," said Sally Stroup, assistant secretary for postsecondary education.

Rep. John Boehner, R-Ohio, chairman of the House Education and Workforce Committee, is sponsoring legislation to scrap the locked-in consolidation loan rates in favor of variable-rate repayment. Doing so will "expand college access for low- and middle-income students" instead of "higher-income college graduates," he said.

The drawbacks of consolidation? You only get one chance to consolidate student loans and must start repaying once you do, although some lenders give new graduates the six-month grace period to start paying so long as they lock up a consolidation loan by June 30.

Also, loan consolidation isn't for everyone:

Most lenders set a minimum loan balance of $7,500 for consolidation, with repayment extended according to the consolidation total and other education debts.

Grads shouldn't consolidate federally subsidized Perkins loans with other college debt if they plan to cancel all or part of their debt through loan-forgiveness programs, advises Kalman Cheny, author of "Paying for College Without Going Broke."

And, finally, don't consolidate if you've paid down your student loans to the point where consolidation doesn't make financial sense.