The two policy positions signaled an effort by Romney to move to the political center as he works to court critical general election swing voters - including young voters and Hispanic voters - after a brutal primary fight.
"I think young voters in this country have to vote for me if they're really thinking of what's in the best interest of the country and what's in their personal best interest," Romney said as he stood next to Rubio, R-Fla., and answered reporters' questions for the first time since effectively securing the GOP presidential nomination.
House Republicans oppose legislation to temporarily extend low-interest rates for student loans. Obama has been pushing Congress for the extension and planned a three-state tour this week to warn students of the potential financial catastrophe they will face if Congress fails to act.
Romney refused to embrace a Rubio proposal that would allow young illegal immigrants to remain in the United States to work or study. He did say there were provisions to "commend" it and that his campaign would "study the issue.
Romney said during the South Carolina primary that all illegal immigrants should return to their home country and get in line to be eligible for U.S. citizenship. Rubio's still-evolving bill would allow young illegal immigrants who graduated from high school and have no criminal record to obtain a nonimmigrant visa. They could stay in the United States, obtain a drivers' license and work or continued their studies but would have no special path to citizenship.
Romney's answers illustrate the careful line he has to walk as he transitions from the primary to the general election, where he'll have to tussle with Obama for support from the Hispanic, female and young voters who propelled Obama to victory in 2008.
Obama, meanwhile, has to hang on to those constituencies. His tour through North Carolina, Colorado and Iowa on Tuesday and Wednesday is intended to rally young supporters.
Romney's language on loans, for example, was distinctly different from the answer he gave when he was last asked about the issue. Prior to the Illinois primary on March 20, he told a young woman concerned about student debt to "get ready for President Obama's claim."
"I know he's going to come up at some point and talk about how he's going to make it vanish. And that's another, 'Here, I'll give you something for free.' And I'm not going to do that," Romney said. During that same answer, he said he wanted to keep interest rates low.
Romney also tacked to the right on immigration during the primary. In recent days, he's been highlighting Hispanic concerns at events while leaving out much of the rhetoric he embraced earlier this year. He said Monday that he would outline additional changes to the immigration system in the coming months, particularly with the visa system that governs who is allowed to work in the U.S.
"I anticipate before the November election we'll be laying out whole series of policies that relate to immigration, and obviously our first priority is to secure the border, and yet we also have very substantial visa programs in this country," Romney said. "How we adjust our visa program to make it fit the needs of our country is something I'll be speaking about down the road."
Still, he wouldn't go so far as to embrace Rubio's immigration proposal. Rubio has said his goal is to craft a Republican compromise on the so-called DREAM Act that Romney could support. The DREAM Act, which has languished on Capitol Hill, would provide a path to citizenship for some young illegal immigrants who attend college or serve in the military.
The Cuban-American senator is considered a top potential pick for vice president. He's the latest in a string of possible running mates to campaign with Romney and is the first to get an audition since former Sen. Rick Santorum, R-Pa., left the race and Romney staffers formally began organizing the process of searching for a No. 2.
Romney declined Monday to say if Rubio was on his list of vice presidential candidates. He said his campaign is still setting up the infrastructure that's required to scrutinize potential nominees, including hiring legal and accounting staff.
The former Massachusetts governor also refused to say whether Rubio is experienced enough to serve as his No. 2. Romney often criticizes Obama, who was a first-term senator when he was elected president, as a "nice guy" who is "in over his head," implying that the Democratic incumbent didn't have the experience he needed for the job.