Liberal critics complain, not without reason, that this measure sells out future students at the expense of current ones. Interest rates on federally subsidized student loans would be related to the 10-year Treasury note, an index proposed by a bipartisan group of senators as well as by President Barack Obama. That means rates will remain low — less than 4 percent for undergraduates — so long as interest rates remain low. But if the economy improves and interest rates rise, as economists and congressional budget analysts expect, the rates will rise. The legislation caps rates at 8.25 percent for undergraduates (and 9.5 percent and 10.5 percent, respectively, for graduate students and parents), meaning that future students may wind up paying even more than the doomsday rates that Congress is seeking to avoid today. Effectively, the bill pays for keeping rates low now by letting them rise later.