If you want to trace the weakness in the US economy to one root problem, here it is in a word: debt.

To many economists it's a conclusion that's hard to avoid. The lingering effects of a credit boom and bust continue to hinder a strong economic recovery.

Lest we forget, debt problems were the precipitating cause of the deep contraction of 2008. And still today, US consumers remain saddled with historic debt burdens. What's more, government borrowing has soared to worrisome levels, and banks face piles of bad loans – a problem that makes them less able to provide new credit to the economy.

Of course, borrowing in itself isn't necessarily good or bad. When used with moderation and for useful purposes, credit is actually a major fuel for economic growth. The word "leverage," employed by finance types as a synonym for debt, rightly implies a tool – a kind of force multiplier.

But when debts grow too large, the multiplying effects can turn negative. And the fallout can be stagnation that lasts for years. That's the risk facing the US and world economies today.

The urgency of the debt issue is visible in Congress, as a 12-lawmaker "super committee" has struggled without success to strike a deal taming chronic federal deficits. It's visible in the Obama White House, which recently stepped up efforts to help at-risk mortgage borrowers refinance troubled home loans. And it's apparent in Europe, where efforts to contain a government-debt crisis are at a critical stage – with spillover implications for the rest of the world.

But if the problem of debt is simple to identify, it's mighty hard to fix. Divided power in Washington, with Republicans and Democrats not seeing eye-to-eye on policy, is just one part of the challenge.

"We're not in an easy position," says Desmond Lachman, an economist at the conservative American Enterprise Institute in Washington. "The policy options aren't that obvious, even if you didn't have the political constraint."

If not addressed, public- and private- debt levels will stand as an ongoing obstacle to growth in the United States, as well as Europe and Japan, concludes a September report by economists at the Bank for International Settlements in Basel, Switzerland.

Already, it's clear that the US economy has been weakest – both during and after the recession – in regions where household debts are highest. That's the conclusion of county-level analysis by Amir Sufi of the University of Chicago, working with Atif Mian of the University of California, Berkeley, and Kamalesh Rao of MasterCard Advisors.

Even after two years of recovery, debt remains the economy's major challenge, says Mr. Sufi.

Debt may be dampening growth in a variety of ways, including:

Tighter credit. This affects consumers and small businesses through things like lower credit-card limits, closer scrutiny of mortgage applications, and higher bank fees since the recession. Part of the reason: Banks themselves are far from healthy, and regulators are calling on banks to boost their capital reserves as high rates of default on home loans persist.

A bust for family wealth. Before the recession, consumers were busy extracting cash from their houses (through home-equity loans and refinancing) – pumping cash directly into the economy. Now, after a drop in home values, many families with diminished net worth are trying to save more and spend less.

Diminished mobility. When people feel free to relocate, that helps the economy grow faster by using available labor in the most efficient ways. But between 2010 and 2011, a record low percentage of the population moved, according to recently released census numbers. One important reason appears to be inertia from the housing bust. Many people are staying put because they can't sell their homes at a price that would pay off their mortgage.

Leaner government spending. With many American voters worried about rising public debts, and credit-rating agencies issuing their own warnings, the climate for government spending has shifted sharply since 2009. Whether or not they believe more fiscal stimulus programs (like tax cuts or infrastructure spending) would be helpful right now, most economists say cuts in federal spending will reduce growth of the gross domestic product in the near term. Taking both state and federal governments into account, US fiscal policy is already restricting growth, by some estimates.

All this doesn't mean debt is the only obstacle in the path of a stronger recovery.

Some economists see other problems at the forefront. One camp, for example, argues that US government debts remain manageable in size (for now), and therefore the big policy failure is that fiscal stimulus programs haven't been big enough. Another camp argues that the missing ingredient for recovery is to get government out of the way by putting new regulations on hold (including the Obama health-care reforms) and by signaling resolve to restrain federal spending and keep future tax rates low.

Brian Bethune, an economist at Amherst College in Amherst, Mass., agrees with the notion that one big drag on consumers and businesses is uncertainty – doubts about everything from tax and health-care policy to the future trajectory of the economy. But he sees this problem as intertwined with debt.

"The two kind of feed on each other," Mr. Bethune says, and are "part of the same overall malaise that we're in."

The debt burdens don't halt US growth outright. The economy appears to be expanding at an annual pace of about 2 percent. The problem is, that hasn't been fast enough to bring unemployment down significantly, because the labor force is growing and so is worker productivity. And the tepid growth leaves the economy vulnerable to a recession if a new head wind arises.

A recent Heartland Monitor poll found some 47 percent of borrowers saying the downturn has encouraged them to pay off debt or not take on new debt, even if that means spending cutbacks. And since the recession began, the amount of income that households must devote to monthly debt payments has fallen from 14 percent of income to 11 percent. "It's like having 3 percent more income to spend," says Karen Dynan, an economist at the Brookings Institution in Washington.

By other measures, millions of families still have a long way to go. Despite all the defaults and foreclosures in the past four years, total mortgage debt today is nearly $10 trillion, down only 6 percent from its peak year of 2007.

So what can be done? Some leading policy options would target mortgages and the housing market directly.

President Obama recently announced changes in a program to reduce monthly payments for at-risk homeowners. The goal is to offer refinancing to some of the 11 million borrowers who owe more than their homes are worth. Moody's Analytics estimates that the new "refi" push could help 1.6 million households, bringing the total served by Mr. Obama's Home Affordable Refinance Program to 2.85 million.

Some economists call for more aggressive re-financing, or new incentives to bring buyers into the housing market – whether as occupants or landlords.

Sufi, at the University of Chicago, says he supports considering ambitious plans. He also cautions against viewing any as a quick fix.

In fact, by some estimates a large-scale refinancing effort might allow GDP to grow about half a percentage point faster – helpful, but still not an enormous benefit.

That means policymakers might need to consider a range of other policies to get the recovery back on track:

•The Federal Reserve could attempt more unconventional means to pump monetary fuel into the economy, although economists are divided over whether such an effort would work.

•On fiscal policy, a credible long-term plan to reduce US budget deficits could be a confidence boost for consumers and businesses, while not necessarily causing a big immediate plunge in federal spending.

•Other moves might help the economy grow faster regardless of how long the debt drag lasts. Streamlining the tax code or taking steps to promote innovation are examples.

Even small successes could be important, helping the economy achieve what Bethune calls "escape velocity." The more jobs and incomes grow, the easier it will be for debtors and home prices to revive.