My grandmother, Big Mama, had a key financial rule that I’ve followed throughout my life.

You can manage without a telephone, she would say. You can take the bus and get by without a car. But you can’t live comfortably if don’t have a roof over your head. Big Mama always made sure she paid her mortgage and on time.

Thankfully, Big Mama, who raised me, never had to skip payment on another bill in order to cover her mortgage. If it had come to that, there’s no question which bill would have been paid first.

But a new study shows many people, when faced with a financial crisis, are not putting their mortgages first.

TransUnion, one of the big credit bureaus, recently released a report that found an increasing number of consumers are choosing to pay their credit-card bills before their monthly mortgages.

The percentage of people delinquent on their mortgages but current on credit cards jumped to 6.6 percent in the third quarter of 2009, up from 4.9 percent in the third quarter of 2008.

“I think the biggest message that the data shows is that consumers’ priorities have changed,” said Sean Reardon, the author of the TransUnion study and a consultant for the credit bureau. “This is really a reflection of the housing bubble bursting and the ripple effect of the recession.”

Seismic shifts

It was in the first quarter of 2008 that the percentage of consumers current on credit cards and delinquent on mortgages surpassed the percentage of consumers up to date on their mortgages and delinquent on credit cards, TransUnion reports.

“The implosion of the mortgage industry over the last 24 months, the resetting of adjustable-rate mortgages and the weak job market have all come together to redefine how consumers are managing their finances and meeting or not meeting their credit obligations,” said Ezra Becker, director of consulting and strategy in TransUnion’s financial services business unit.

Many people see their credit card as an emergency source of funds. They may not be able to afford a mortgage payment but they can make a minimum credit-card payment. For them, it’s not about buying flat-panel televisions or toys for their kids. Instead, they are using credit to buy food or gas or pay for other basic necessities. When faced with a choice, they are opting to pay on their credit-card accounts so that reservoir of money doesn’t get snatched away.

For the study, TransUnion looked at consumers who had at least one credit card and one mortgage. The company examined 30-day credit card and mortgage delinquency data.

The payment hierarchy shifts are even more pronounced in California and Florida, two states that have seen high foreclosure rates and significant decreases in home prices.

TransUnion found that the percentage of consumers in California who are delinquent on their mortgages but current on their credit cards was 10.2 percent in the third quarter of 2009, up from 3.5 percent in 2007. In Florida, the increase went from 5.1 percent for the same period to 12.4 percent.

Little relief in sight

The financial news continues to be troubling, signaling that this trend may not turn around soon. In the week ending Jan. 30, the Labor Department said the number of laid-off workers filing initial claims for unemployment benefits was 480,000, an increase of 8,000 from the previous week. Forecasters had expected new claims would drop.

A record 2.8 million U.S. properties received foreclosure notices in 2009, up 21 percent from 2008 and 120 percent from 2007, according to a 2009 year-end report from RealtyTrac, which tracks foreclosure activity throughout the country.

“In the long term, a massive supply of delinquent loans continues to loom over the housing market, and many of those delinquencies will end up in the foreclosure process in 2010 and beyond as lenders gradually work their way through the backlog,” said James J. Saccacio, chief executive officer of RealtyTrac.

Reardon said in an interview that many people are figuring they may lose their homes, so they reason: Why pump more money into the mortgage? They cling to the notion that the plastic is their savior.

“It used to be people kept cash in the coffee can for an emergency,” Reardon said. “But times have changed. People don’t have coffee cans. Plastic has become their coffee can.”

I hope this trend is only temporary. Relying on your credit card is like having a life jacket with a slow leak. It may keep you afloat for a little while, but the protection is short-term. You’ll still sink.