The nation’s public colleges and universities were founded on the principle that everyone should be able to afford a higher education — not just wealthy elites.

But that principle is being challenged by states’ dwindling investment in their public institutions of higher education, leading to tuition hikes that create obstacles for students from low-income and middle-class families, experts say.

“In the 1960s through the 1970s, there was a clear investment from the state and support for this idea that, through public dollars and subsidized loans, and the student working over the summer or part-time, you could pay for higher education,” said Michael Mitchell, a policy analyst at the Center on Budget and Policy Priorities, a progressive think tank.

But in recent decades, tuition costs have risen as public investment has fallen, with the trend worsening during the economic downturn that began in 2008.

In the decade from 2002–03 to 2012–13, states’ average per-student funding for public higher education declined by 23 percent in real dollars, said Sandy Baum, a professor at George Washington University and co-author of the College Board’s “Trends in College Pricing 2014.”

And, in just the six years from 2007–08 to 2013–14, states’ average funding per full-time student fell from $9,290 to $7,161 in inflation-adjusted dollars, Baum said.

The resulting increases in tuition have created a double whammy for many parents of modest means, who are shouldering higher college costs at a time when their own salaries have remained stagnant. One result is that many students are graduating with a punishing debt load

At the same time, the greater need for young people to get a college degree to land a good job has led to an increase in enrollment at public colleges, Baum said.

Since 2008, she said, “enrollment expanded really rapidly and per-pupil funding declined.”

New York State cut overall public higher education funding by 11.1 percent per full-time student from 2008 to 2014. Over the same period, average per-student tuition costs at the state’s four-year public institutions rose by $1,215, according to Mitchell of the Center on Budget and Policy Priorities.

Perhaps most telling is this: In 2002, New York State funding covered 63 percent of SUNY’s operating budget, with the other 37 percent paid through students’ tuition and fees, said Jamie Dangler, the vice president for academics at United University Professions, the union representing SUNY employees at four-year institutions. Ten years later, those percentages had flipped: 63 percent of the SUNY system’s budget was paid by tuition and fees, and 37 percent by the state.

Investments in public higher education used to have broad, bipartisan support, Mitchell said.

No longer.

This year, a number of Republican governors — in Louisiana, Arizona, Wisconsin, Kansas and Illinois — proposed cuts in their states’ higher education spending. At least one Democratic governor, Dannel Malloy in Connecticut, has called for the same.

Critics say these state leaders are making a big mistake.

College graduates contribute increased earnings and tax revenues to states’ coffers, said Walter McMahon, a professor emeritus of economics and education at the University of Illinois, in an article in Stateline, the daily news service of the Pew Charitable Trusts.

“Spending on education is really an investment,” McMahon said. Cutting this funding to close budget gaps is “very, very shortsighted.”