CONCORD, N.H. — New Hampshire ranks first in student-loan debt, and now Republican presidential candidate Mitt Romney is seizing on that fact to argue that President Obama has let students down.

The Republican Party released a Web ad juxtaposing video of New Hampshire college students describing their staggering debt with what it characterized as Obama’s failed promises to deliver relief.

While the truth is far more complicated, Romney’s campaign plans to make the same argument in other states, spokesman Ryan Williams said.

U.S. seniors who graduated with student loans in 2010 owed an average of $25,250, up 5 percent from the previous year, according to the Institute for College Access and Success, an advocacy group that compiles data reported by colleges and universities. New Hampshire’s average was just above $31,000, the highest in the nation.

In Massachusetts, which ranks 12th, the average debt carried by college graduates increased by nearly 25 percent when Romney was governor from 2004 to 2007.

And while Romney has seized on New Hampshire’s ranking, that state has been in the top five each year since 2005 for a variety of reasons, many of which have nothing to do with the president or the federal government.

One significant factor is the state’s mix of colleges and universities: The percentage of New Hampshire students who attend private schools is higher than the national average, 40 percent compared to 29 percent nationally. Private schools generally are more expensive than public schools, and New Hampshire’s private schools tend to be more expensive than private schools in other states.

New Hampshire’s public colleges and universities also are more expensive than other state schools, which is illustrated by another ranking that likely contributes to the state’s high debt level: it is last in per capita state support for public higher education.