Thinking about borrowing against your 401(k) account to finally buy the iPod you've been lusting after, or that snazzy new cell phone with built-in camera and Web access?

Well, before taking the plunge, you may want to pause a moment and consider your total debt level. If you are anything like the typical consumer, the numbers may look pretty scary.

According to data from the Federal Reserve, U.S. households had $9.7 trillion in mortgage and consumer credit debt at the end of June.

Sound like a lot? It is.

The figure represented more than 80 percent of the nation's gross domestic product through the end of the second quarter and more than 100 percent of total disposable household income of about $8.6 trillion. It is also about 21 times the burden shouldered by U.S. households in 1970.

In short, Americans are swimming in debt and getting in deeper by the minute. Personal bankruptcies are running at record highs.

Meanwhile, the personal savings rate is below 1 percent and flirting with a record low. Taken together, these numbers trouble many economists who worry that Americans, especially at lower income levels, do not have nearly enough set aside for emergencies or to prepare for retirement.

"Based on the direction that things have been going, and the continuing crumbling of the private pension system, in 25 years, especially in lower income brackets, people who are trying to retire are going to have a very hard time of it," said Alex Baker, who has studied the issue extensively for the liberal Century Foundation.

Of course, in many cases, rising household debt has been easily outpaced by the dramatic run-up in home values. Meanwhile, historically low interest rates have allowed millions of Americans to treat their homes as cash machines, refinancing mortgages while taking out equity to pay for home improvements or general spending.

Sung Won Sohn, chief economist at Wells Fargo, notes that about 70 percent of current household debt comes from mortgages, most of which are fixed at attractive interest rates. "There is a hard asset, hopefully appreciating in value, behind most of the debt," Sohn said.

But Sohn and many others worry about what could happen if the real estate market, as some fear, has in fact taken over from technology stocks as the investment bubble of the moment. If home prices drop, as they already have in some affluent areas such as Orange County, Calif., it could both wipe out large amounts of wealth and cut into available household cash. With incomes continuing to rise slowly, such an event could force households to dramatically cut back spending, which could in turn derail the consumer-dependent economy.

Sohn, however, said he believes the prospect of a nationwide real estate crisis is unlikely. Instead, he said the drop would probably be limited to affluent areas on both coasts, including the District.

"I think the popping of the real estate bubble will be localized," he said. "But I think the overall risk" that a drop in real estate prices poses to the economy "is as high as it's ever been, that I can remember."

Another worry cited by economists is the growth in popularity of adjustable-rate mortgages and interest-only mortgages. Both offer the lure of lower monthly payments, at least at first. But, especially in the case of interest-only mortgages, the payments can spike dramatically after a few years.

Interest-only mortgages, previously marketed only to the affluent who used them for tax or investment purposes, are now being made widely available, especially to lower-income buyers looking for small monthly payments. The loans allow home buyers to pay no principal for several years, with monthly costs spiking when the principal kicks in. Many of these loans also have adjustable rates, which can add to the financial sting as rates rise.

According to data cited by the newsletter Inside Mortgage Finance, $27.82 billion worth of sub-prime, interest-only mortgages were packaged as securities and sold to investors through September of this year, up from $2.54 billion during the same period last year.

"Make no mistake about it: Interest-only loans are the hottest thing going in the sub-prime market right now," the newsletter said.

Meanwhile, a Consumer Federation of America study this summer found that adjustable-rate mortgages are disproportionately popular among lower-income and minority home buyers, many of whom may find themselves unable to meet payments as rates rise.

"Given the high probability of interest-rate increases, an adjustable-rate loan made to a family which can barely afford the initial monthly payments represents a ticking time bomb," CFA Executive Director Stephen Brobeck said when the report was released.

The question is, How many other ticking time bombs are out there?