"When you have a financial crisis like that, it's years of digging out," the Microsoft chairman said Monday during an interview on ABC's Good Morning America.
"The budget's very, very out of balance," Gates warned.
"And even as the economy comes back, without changes in tax and entitlement policies, it won't get back into balance. And at some point, financial markets will look at that and it will cause problems," Gates added.
Gates' comments come three days before Microsoft is slated to announce earnings for its fiscal second quarter. Analysts surveyed by Thomson Reuters expect the company to post earnings per share of 59 cents, on revenue of $17.79 billion.
In 2008, Microsoft posted second quarter earnings of 47 cents on $16.63 billion in revenue.
The interview coincided with the publication of Gates' annual letter from his charitable organization, the Bill & Melinda Gates Foundation. In the letter, Gates said he talked to co-trustee Warren Buffett "more than ever" during the past year to gain a better understanding of the financial meltdown.
"Although the acute financial crisis is over, the economy is still weak, and the world will spend a lot of years undoing the damage, which includes lingering unemployment and huge government deficits and debts at record levels," Gates wrote.
Still, there are indications that some markets are stabilizing and are in line for growth.
Research firm Forrester is calling for tech spending in the U.S. to grow 6.6% this year, to $568 billion, after being down 8.2% in 2009. Worldwide spending will jump 8.1% to more than $1.6 trillion, following a decline of 8.9% last year, according to Forrester.
Microsoft shares were up 1.42%, to $29.37, in early trading Monday as stock markets rebounded from Friday's sell off.
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