WASHINGTON – Student loan rates will double to 6.8 percent on July 1 if Congress doesn’t settle on a new plan soon. But disagreements flared Thursday, not only between the two parties, but between a veteran Democrat and President Obama.

Sen. Tom Harkin, D-Iowa, chastised his own party’s leader over the details of the president’s solution to the problem. Obama in his budget plan earlier this year proposed a market-based student loan rate, similar to a Republican proposal, but at a lower rate and with a different protection for future increases.

Harkin, chairman of the Senate Committee on Health, Education, Labor and Pensions, has proposed an alternative that would freeze the borrowing rate at 3.4 percent for two years while Congress worked out a long-term plan.

“I’ve got to tell you, I’m very upset with President Obama and the Republicans,” Harkin said Thursday. “This is the first president since 1958, since this came into being, that has advocated changing the basis from 91-day T-Bill (Treasury bill) rate to a 10-year Treasury bond. It’s a lot in terms the interest kids are going to have to pay.”

He also said the president’s plan would hurt low-income students.

“I’m telling you,” Harkin said, “the African-American community better look at this, and what this is going to mean to low-income students all over America, who are disproportionately black, and what it means in terms of how much they’re going to have to pay for these government loans.”

Harkin also said Obama was the first president who would lift the cap on student loan rates. Instead, Obama would offer income-based repayment plans for all borrowers so that monthly payments would be manageable.

Obama’s plan bases the student loan interest rate on the 10-year Treasury rate and adds 0.93 percent. House Republicans tie it to the same rate but add 2.5 percent. Obama also called for locked-in rates for the life of the loan, rather than a readjustment every year as House and Senate Republicans have proposed.

House of Representatives Republicans say rates should be capped at 8.5 percent.

House Speaker John Boehner, R-Ohio, also weighed in on the issue Thursday, claiming that Obama and the Democrats “have decided to deliberately allow rates to rise.” He said the Republican plan was similar to the president’s, “but the Democrat-controlled Senate has refused to pass it.”

The president criticized the Republican plans last month, saying that because they didn’t lock rates in, students starting school next year would end up paying more over their college years than if Congress did nothing and rates simply doubled. Currently, Congress sets the rate every year.

Students increasingly are taking out loans to cover college costs as tuition and fees go up. If rates double, as they will next month should no action occur, students would pay an additional $1,000 over the life of the loan.

The debate came up on the Senate floor Thursday, as well.

Sen. Elizabeth Warren, D-Mass., asked for a unanimous consent on the Democrats’ two-year extension of the 3.4 percent rate, paid for by closing some tax loopholes. Under Senate rules, if one member objects to such a motion it can’t be done, and Sen. Richard Burr, R-N.C., objected. Burr asked for unanimous consent to pass a bill that he said was similar to Obama’s proposal. Warren objected, so there was no vote on the Republican proposal, either.