Correction: An earlier version of this article incorrectly said that half of students who take out loans to enroll in two-year for-profit colleges never finish. The statistic applies to borrowers at four-year for-profit colleges. The article also misstated the name of the organization that did the study. It is the Education Sector, not the Education Trust. This version has been corrected.

As the nation amasses more than $1 trillion in student loans, education experts say a vexing new problem has emerged: A growing number of young people have a mountain of debt but no degree to show for it.

Nearly 30 percent of college students who took out loans dropped out of school, up from fewer than a quarter of students a decade ago, according to a recent analysis of government data by think tank Education Sector. College dropouts are also among the most likely to default on their loans, falling behind at a rate four times that of graduates.

That is raising new questions about the wisdom of decades of public policy that focused on increasing access to higher learning but paid less attention to what happens once students arrive on campus. And some education experts have begun to argue that starting college — and going into debt to pay for it — without a clear plan for a diploma is a recipe for disaster.

“They have the economic burden of the debt but they do not get the benefit of higher income and higher levels of employment that one gets with a college degree,” said Jack Remondi, chief operating officer at Sallie Mae, the nation’s largest private student lender. “Access and success are not linking up.”

The Obama administration says it is trying to address the issue by coupling its goal of ensuring that high school students are prepared for at least one year of higher education with new targets for college graduation rates.

The plight of “non-completers” has grown in magnitude as student debt tops $1 trillion, according to the Consumer Financial Protection Bureau. In addition, the sputtering economy has forced a growing number of students to make difficult choices between the benefits of a degree and the burden of paying for it. More students are balancing their studies with full- or part-time jobs or signing up for a reduced course load to save money, increasing the likelihood that they will not graduate.

According to a 2009 study by Public Agenda, half of college dropouts said work was a major factor in their decision. Only a quarter said they had spent too much time socializing.

‘Money and time’

“In the end, it’s about money and time,” said Anthony Carne-vale, director of the Center on Education and the Workforce at Georgetown University. “There’s almost a synergy between the two that will knock you out of school.”

The cost to the economy is roughly half a trillion dollars, he said. Although college dropouts make more than those with only a high school diploma, he said they earn about a million dollars less than college graduates over their careers.

Malainie Smith spent a year at a small liberal-arts college in Massachusetts before deciding to go to nursing school. She was halfway through her program at Simmons College in Boston when she took what she thought would be a break of one semester. When she tried to return, she found she could no longer get a loan.

Smith said that left her in a Catch-22 situation. She had to quit school but still owed about $100,000 to the Vermont Student Assistance Corp. (VSAC), a public nonprofit student lender. Her monthly payments are about $400. Three years after she left Simmons, she is now a waitress — a recent promotion from her position as a hostess.

“I’m not getting high-end-

paying jobs,” Smith said. “There’s more potential than this.”

Scott Giles, a vice president at VSAC, said he could not discuss the details of Smith’s situation, citing privacy reasons. But he said the lender often uses the flexibility of its status as a public nonprofit to accommodate students in need.

“We want all of these people to not only get into school but actually complete,” he said. “We bend over backwards to try and make sure that that’s possible.”

Still, Giles said part of his organization’s mission is to ensure that students have the chance to go to college, even though it knows that some of them will never finish. The benefits may take a generation to play out, he said: Students whose parents attended at least some college are more likely to enroll themselves, according to his group’s research.

“There are ways in which the access agenda and the completion agenda are at odds,” he said. “Folks have defined failure to obtain a degree as just that — failure. But that doesn’t necessarily mean that the resources you put into that student up to that point were wasted.”

Burgeoning for-profit sector

College enrollment has swelled by 38 percent during the past decade to more than 20 million, according to government data. But lawmakers and regulators have begun casting a wary eye on the burgeoning market of for-profit institutions with low graduation rates and high student debt loads.

According to Mark Kantro-witz, a student loan expert and founder of FinAid.org, students who receive a bachelor’s degree from a for-profit college will have an average debt of more than $41,000. Students graduating from public universities are expected to have roughly half that debt.

Not only do their students amass more debt, but for-profit colleges also saw the biggest jump in borrowers who drop out, although every type of institution saw increases. A study by the Education Sector found that more than half of students who take out loans to enroll in four-year for-profit colleges never finish. At traditional nonprofit and public schools, the percentage of students with loans who started college in 2003 and dropped out within six years is about 20 percent.

By comparison, about 8 percent of Americans between the ages of 16 and 24 don’t have a high school degree, according to government data.

“As college became a mass institution in America, it started looking like high school. But unlike high school, we didn’t build a system that was designed to keep people in,” Carnevale said. “If we had a 40 percent dropout rate in high school, we’d think we were in a national crisis.”

(The Post Co. owns the for-profit education company Kaplan, Inc., which provides more than half of the parent company’s revenue.)

The Obama administration said it has made increasing the college graduation rate by 2020 one of its top educational priorities. Some schools have also tried to streamline majors and course offerings to help ensure students stay on track. Education experts say that many students are not prepared for the more rigorous course work in college, and that many schools do not offer enough guidance for young people trying to navigate the first steps of their adult lives. As a result, students may not see the payoff in finishing college.

Marian Castelli of Connecticut said her daughter dropped out of the University of Hartford after one year, in part because she was racking up more debt than she thought she could afford. Her daughter studied dance performance and was on the dean’s list but suffered multiple injuries. And with tuition of $20,000 a year, every day mattered.

Castelli said she recalled her daughter telling her, “I don’t think I want to go back to college. I don’t know how I’d ever pay off $80k in debt with a four-year degree.”

Castelli responded, “I couldn’t argue with that.”