ABC News’ Cara Newlon reports:

Senate lawmakers say that a compromise to prevent student loan interest rates from doubling before the impending July 1 deadline appears unlikely.

“If I were a betting person, I’d say that’s something we’ll come back and attempt to fix retroactively,” Sen. John Thune, R-S.D., told ABC News.

If the Senate fails to reach an agreement, interest rates on new Stafford student loans will double from 3.4 to 6.8 percent. The doubling would affect the 7 million students who receive Stafford loans, which serve only the neediest of students.

The Senate’s effort to pass comprehensive immigration reform legislation, which is expected to be put to a vote by the end of this week, has consumed most of the bandwidth in the chamber.

“We’re working right through immigration,” said Senate Majority Leader Harry Reid, D-Nev. “We are going to wrap up immigration either Thursday or Friday. The only question now is whether we can come up with a list of amendments. And I think both sides want to do that, but having said that, I don’t know we can do it.”

“We probably can’t get it done this week,” said Sen. Tom Harkin, chairman of the Senate Health Education, Labor and Pensions Committee.

Harkin’s original proposal, which was outvoted in the Senate, would keep rates at 3.4 percent for two years.

A bipartisan coalition of senators reportedly began working on a compromise last week which would link interest rates to financial markets and fix those rates for the life of the loan. The plan, developed in talks by Sen. Joe Manchin, D-W.Va., Sen. Tom Coburn, R-Okla., Sen. Angus King, I-Maine, and Sen. Lamar Alexander, R-Tenn., would leave rates at about 3.8 percent, according to the Associated Press. It would not include a cap on interest rates.

Manchin’s office would not comment on the proposal, and King’s spokesman Crystal Canney said only that they “are still working on it.”

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