The growing student loan burden carried by millions of Americans threatens to undermine the housing recovery’s momentum by discouraging, or even blocking, a generation of potential buyers from purchasing their first homes.

Recent improvements in the housing market have been fueled largely by investors who snapped up homes in the past few years. But that demand is waning as prices climb and mortgage rates rise. An analysis by the Mortgage Bankers Association found that loan applications for home purchases have slipped nearly 20 percent in the past four months compared with the same period a year earlier.

First-time buyers, the bedrock of the housing market, are not stepping up to fill the void. They have accounted for nearly a third of home purchases over the past year, well below the historical norm, industry figures show. The trend has alarmed some housing experts, who suspect that student loan debt is partly to blame. That debt has tripled from a decade earlier, to more than $1 trillion, while wages for young college graduates have dropped.

The fear is that many young adults can no longer save for a down payment or qualify for a mortgage, impeding the housing market and the overall economy, which relies heavily on the housing sector for growth, regulators and mortgage industry experts said.

“This is a huge issue for us,” said David H. Stevens, chief executive of the Mortgage Bankers Association. “Student debt trumps all other consumer debt. It’s going to have an extraordinary dampening effect on young peoples’ ability to borrow for a home, and that’s going to impact the housing market and the economy at large.”

Stephanie McCloskey, 26, said she feels the pinch. Two years out of college, McCloskey was confident that she could take out a mortgage and buy a townhouse in Gaithersburg, Rockville or maybe Frederick — until she met with a lender last month.

That’s when she realized she would not qualify for a mortgage large enough to pay for a home in the Maryland cities she was eyeing. According to her lender, the $500 she ponies up each month to repay her $30,000 student loan eats up too much of her income.

“I didn’t know anything about buying a house when I was taking out a student loan, so it’s almost like I am being blindsided by a decision I had to make years ago,” said McCloskey, an administrative assistant.

New federal rules

The lending climate has become less forgiving for those carrying student debt, and that’s unlikely to change anytime soon.

Federal rules that took effect last month grant mortgage lenders broad legal protections as long as they do not approve loans for prospective buyers whose total monthly debt exceeds 43 percent of their monthly gross income. The overarching goal is to protect borrowers against lender abuses.

But the rules could also make it difficult for some buyers with student loans to obtain a mortgage. Take someone seeking a $626,000 loan with a 4.5 percent interest rate to buy an $800,000 house.

If that person earned $125,000 a year and had a $450-a-month car payment, he or she would fall within the limit, said Phil Denfeld, a vice president at First Heritage Mortgage in Fairfax. But add a $100 student loan payment to the mix, and the debt-to-income ratio could climb above the new restriction.

This threshold already applies to some types of loans, including “jumbo” mortgages, which exceed $625,500 in the Washington area. But it will not apply to other types of loans for several years.

“This change can affect a wide range of people with student debt. Graduate students, law students or even parents who’ve taken on their kids’ student loan debt,” Denfeld said. “I had one parent who was trying to refinance his house, but he’d taken out a student loan to pay for his child’s college education, and his debt-to-income ratio was too high.”

Without help from her parents, Melissa Nussbaum probably could not have bought her D.C. condominium two years ago, she said. After graduating from Georgetown University with a master’s degree — and $75,000 in student debt — Nussbaum said she struggled for years to save for a down payment. Her parents came to the rescue.

“I imagine that most people don’t have that kind of opportunity where they can go to their parents and have them help,” said Nussbaum, 39. “I know people who are getting rid of their student debt by moving abroad to work in a developing country [for tax benefits and cost savings] so they can pay off their debt more quickly.”

Of the 20 percent of first-time buyers who said it was difficult to save for a down payment, 54 percent said student loans made it tough to save money, according to a recent survey by the National Association of Realtors. About half of the people polled in another of the group’s surveys said student debt was a “huge” obstacle to buying a home.

Recession’s ‘aftershocks’

The Consumer Financial Protection Bureau sounded the alarm about this trend in 2012 and did so again in November. Speaking before the Federal Reserve Bank of St. Louis, the CFPB’s Rohit Chopra said that rising student debt “may prove to be one of the more painful aftershocks of the Great Recession,” with implications for the housing market.

“With more and more Americans putting big chunks of their income toward student loan payments, that means they’re less able to stash away extra cash for their first down payment,” Chopra, the agency’s student loan ombudsman, said in an interview.

Now, the Federal Housing Administration, a popular source of low-down-payment loans for first-time buyers, may make it even tougher. Currently, the agency allows the mortgage lenders it does business with to ignore student debt that’s deferred for a year or more when assessing a borrower’s eligibility for a loan. But it may scrap that waiver this year.

Researchers at the Federal Reserve Bank of New York weighed in last year with their own analysis of the student debt problem’s impact. From 2009 to 2012, the homeownership rate fell twice as much for 30-year-olds who had a history of student loans than it did for those without such debt, they said. The finding upended traditional thinking, which held that student debt signaled higher earnings and higher chances of owning a home.

Chris Herbert, research director at Harvard University’s Joint Center for Housing Studies, agrees with those who say the swelling student debt is a concern. But he also says it may not hobble young adults’ access to the housing market as much as some fear.

In his own analysis, Herbert found that student loan debt is not all piled upon recent college graduates. Rather, it is evenly distributed among age groups as of 2010. Also, the median amount borrowed for school by people in their 20s “barely budged” from 2004 to 2010, hovering around $11,000 when adjusted for inflation, Herbert said.

Only a small share of the under-30 crowd is borrowing sizable sums, he said. But the trend in that age range is worrisome: The share of borrowers under 30 with more than $50,000 in outstanding student debt doubled from 5 percent to 10 percent. (Testifying before Congress in 2012, then-Federal Reserve Chairman Ben S. Bernanke said his son would probably graduate from medical school with $400,000 in student loan debt.)

“This could explain why some of them are sitting on the sidelines,” Herbert said. “But it’s a complex issue, and everyone’s struggling to get a handle on what it means for the housing recovery.”