Altman predicted that the default of high-yield debt would fall 4.3 to 6.7 percent.

That jibes with a study released Monday by Moody’s Investor Service, which found from its own records that just $21 billion of debt is coming due this year. The next few years could prove more problematic: more than $700 billion will come due between 2012 and 2014 (emphasis mine).

Defaults in 2009 rose to 10.7 percent. <> How bad was 2009? Mr. Altman pointed out that 43 companies with more than $1 billion in liabilities filed for bankruptcy then, more than in recent years. About 56 percent of companies that offered debt exchanges to investors, offering to swap bonds for newer ones in an effort to gain breathing room for maturities, still ended up filing for bankruptcy.

But since the economy rebounded last year, so did the debt markets, with Mr. Altman pinning the turning point around June or July. Companies that faced tough choices for their debt found themselves able to refinance their obligations, usually by issuing newer bonds.

That the credit markets have led to a new sea of debt could have ramifications for companies that have now taken on too much debt, Mr. Altman warned. As Moody’s also warned, if economic conditions improve, most borrowers will be able to cover their debts. That’s a big if, however.