* Concerns resurface over mortgage bonds
* Apple, IBM slide after disappointing results
* Commodities slide as China plans to hike interest rates
* Indexes down: Dow 1.5 pct; S&P 1.6 pct; Nasdaq 1.8 pct (Updates with details)
By Edward Krudy
NEW YORK, Oct 19 (Reuters) - U.S. stocks posted their biggest loss in two months on Tuesday on fears banks might be on the hook for billions of dollars in souring mortgage bonds.
The afternoon selloff hit investors already reeling from an unexpected credit tightening by China and disappointing financial results from Apple and IBM.
The biggest scare came on news that Bank of America and possibly others may be forced to take back billions of dollars in mortgages that should not have been bundled into bonds.
The broad selloff came on high volume in a pattern similar to last week's when fears over banks surfaced.
"It's reminding investors of what was the main impetus for the horrific selloff we had a few years ago," said Eric Kuby, chief investment officer at North Star Investment Management in Chicago. "If you were recently struck by lightning, you are a little skittish when there is a thunderstorm."
Bank of America shares fell 4.4 percent to $11.80, their lowest close since June 2009, after a Bloomberg report, citing people familiar with the matter, said investors PIMCO and BlackRock, along with the New York Federal Reserve Bank, were seeking to force the lender to repurchase $47 billion in mortgage bonds.
The bank, the New York Fed and PIMCO declined to comment.
The Dow Jones industrial average dropped 165.07 points, or 1.48 percent, to 10,978.62. The Standard & Poor's 500 Index lost 18.81 points, or 1.59 percent, to 1,165.90. The Nasdaq Composite Index fell 43.71 points, or 1.76 percent, to 2,436.95.
The S&P 500 fell the most since mid-August when equities were in a steep selloff. The index closed below its 10-day moving average, which some traders see as a bearish sign.
"A clear break of the 10-day moving average at 1,170 on the S&P 500 will be the catalyst for the start of a real pullback/correction in my opinion," said Elliot Spar, options market strategist for Stifel Nicolaus in Shrewsbury, New Jersey.
In an almost perfect storm for equity markets, China's decision to raise interest rates drove the dollar higher as investors cut exposure to risk, putting downward pressure on commodities and related stocks.
Selling in commodities accelerated as fears in the mortgage market grew. U.S. copper prices finished near the sharply lower levels hit on Tuesday, while crude oil futures fell 4.5 percent to under $80 per barrel.
Oil company Exxon Mobil fell 1.8 percent to $65.12 while the S&P energy index lost 2.4 percent. Industrial company Caterpillar Inc lost 2.1 percent to $78.55 and was among the biggest drags on the Dow.
Gold, which has rallied in recent weeks as a safety play against a weaker dollar, fell nearly 3 percent.
The Arca gold bugs index, which tracks 16 big gold miners, fell 5.1 percent. Barrick Gold was the biggest drag on the index, down 4.9 percent to $45.46.
Apple's shares fell 2.7 percent to $309.49 and weighed on the Nasdaq after iPad sales fell short of some analysts' expectations. Only the day before, Apple shares hit a lifetime high.
International Business Machines Corp fell after it won fewer technology service deals than expected in the third quarter. Its shares were down 3.4 percent at $138.03, even as it announced stronger profits and raised its full-year outlook.
Goldman Sachs Group Inc said net trading revenues fell by more than a third in the quarter, but the company's profits beat analysts' estimates, sending its shares up 2 percent to $156.72.
Investors' jitters coincided with the anniversary of the 1987 stock market crash when the Dow fell over 20 percent in one day.
The CBOE volatility index, a measure of market volatility, rose 8.1 percent in a sign investors may be expecting turbulence ahead.
About 9.83 billion shares traded on the New York Stock Exchange, the American Stock Exchange and the Nasdaq -- above the year's average so far of about 8.77 billion.
Declining stocks outnumbered advancing ones on the NYSE by a ratio of nearly 5 to 1. The ratio was about the same on the Nasdaq. (Reporting by Edward Krudy; Editing by Kenneth Barry)