One in four homeowners in Rhode Island and the New Bedford-Fall River area who bought houses since 2003 owe more on their mortgages than their property is worth, according to new data from economic and real-estate research firms.

The situation, often described as being “under water,” means these homeowners cannot sell their houses to get out from under their debts, or move for a new job. Nor can homeowners with zero equity borrow against their houses to repair a boiler or pay college tuition.

That leaves only one option: cut back on spending.

“There is going to be a sea change in how aggressively households spend from here on in and for a long time to come,” said Mark Zandi, chief economist at Moody’s Economy.com. “We’re going to have to at least match our spending with our incomes, and for many of us whose nest eggs are smaller, we’ll have to start saving.”

During the housing market’s peak, Americans borrowed heavily against the value of their houses to pay for what their paychecks could not. Consumer spending, which accounts for two-thirds of all economic activity, helped to fuel the economy.

Now, strapped homeowners are saddled with houses that aren’t worth what they paid for them, and banks don’t want to lend to them.

“There isn’t a lot of historical precedent about how consumers are going to behave when faced with the double whammy of massively declining home prices, being under water on their mortgages and now seeing the impact of the financial markets on their retirement income,” said Thomas Lawler, a Virginia-based housing consultant.

For homeowners who earn close to the median income — just under $54,000 in Rhode Island last year — their houses are generally their largest asset and, until recently, Lawler said, the main source of their net worth. So if consumers can’t borrow against their house, “what other choice do you have?”

Yesterday, a report by the Commerce Department offered fresh evidence that consumers are, indeed, cutting back. Retail sales plunged in September to their lowest level in three years.

For the last 25 years, consumers have steadily spent more than they earned by borrowing more. By 2006, the savings rate had fallen to nearly zero — down from about 8 percent during the early 1980s.

That was before the housing market soured and the credit markets seized up. House prices nationwide have fallen, on average, 13.3 percent from their peak in the fourth quarter of 2004, according the real-estate research firm Zillow.com.

Nationally, an estimated 12 million households, or 16 percent of all homeowners, owe more on their mortgages than their houses are worth, according to an analysis by Moody’s Economy.com that was reported in The Wall Street Journal.

In the Providence metro area, a similar analysis showed that roughly 27,400 households — or one in four homeowners — who bought their houses during the last five years are under water. (The Providence metro area covers all five counties in Rhode Island plus the New Bedford and Fall River areas in Southeastern Massachusetts.) Moody’s analysis used price estimates from Zillow.com.

“Anyone who bought before 2004 still has gained some value on their home,” said Amy Bohutinsky, vice president for communications at Zillow.com. “Obviously, for people who bought at the market peak, they’re in a little worse situation.”

They are people such as Michelle Hunt and her husband, Eric Flaherty. The couple, both in their 20s with two young children, bought their first house in January 2005. He was working for a housing construction firm; she was answering phones for a corporate help desk and bartending. The couple couldn’t afford a single-family house, so they settled for a two-family with a small yard in Cranston for $277,500.

They paid for the house with a zero-down loan, Hunt said, and $3,000 that Michelle’s mother had loaned her.

“The plan was to buy a house, live in it for five years, and sell it for more,” Hunt said.

That was before house prices plunged.

Now, they still owe $267,000 on their mortgage. The last time Michelle checked Zillow.com, similar houses were selling for about $235,000 — $32,000 less than they owe on their mortgage.

“We always used to talk about what we wanted to do — the vacations we wanted to take,” Hunt said. “Now, I don’t even want to talk about it because it’s depressing.”

Her husband works overtime and weekends at his construction firm, where he builds high-end houses in Newport County. Michelle, who quit her job at CVS when she was pregnant with their daughter, now works part time for $8 an hour at a children’s clothing store and takes care of their children, ages 2 and 9. Their household after-tax income is roughly $45,000 a year. After being offset by the $950 a month in rent from their first-floor tenants, their mortgage payment, including taxes and insurance, is $1,550 per month. They pay $860 a month for their family health insurance plan. Add in groceries, gas, electric bills, cable and their minimum credit card payments, and they barely break even.

“We don’t go out at all,” Hunt said.

They have no money socked away to replace their furnace if it breaks (and it’s more than 25 years old) or their car if it needs to be repaired — and no equity in their house to borrow against. And they’ve already missed one mortgage payment.

Hunt said her parents live in Worcester, in the same house they bought in 1981. Over the years, they put on a new roof, repaved the driveway and refinished the hardwood floors. If Hunt and her husband can’t make their mortgage payments and have to give up the house, she said, her parents would take them in. But that’s a last resort.

“I just would feel like a failure,” Hunt said. “Were just going backwards instead of forwards.”

larditi@projo.com

Correction: A previous version of this story incorrectly referred to one quarter of all area homeowners in the headline.