Heading off a costly rate increase for returning college students, a bipartisan group of senators reached a deal Wednesday that would offer students better rates this fall but perhaps assign higher rates in coming years.The deal would offer students lower interest rates through the 2015 academic year, but then rates were expected to climb above where they were when students left campus this spring.The interest rates would be linked to the financial markets, but Democrats won a protection for students that rates would never climb higher than 8.25 percent for undergraduate students.Graduate students would not pay rates higher than 9.5 percent, and parents' rates would top out at 10.5 percent.The deal was described by Republican and Democratic aides who insisted on anonymity because they were not authorized to discuss the ongoing negotiations by name.A vote on the agreement could come as early as today, although it could be pushed back to the middle of next week depending on the Senate calendar.Lawmakers from both parties called the hike senseless but differed on how to restore the lower rates.Senators cut student loans deal