* Investors focus on Fed comments, indexes near highs
* Facebook volatile after results, Exxon shares higher
* Jobless claims fall slightly less than expected
* Indexes down: Dow 0.3 pct, S&P 0.3 pct, Nasdaq 0.4 pct
NEW YORK, Oct 31 (Reuters) - U.S. stocks fell modestly on Thursday, with investors cautious with indexes near record levels as they digested recent comments from the Federal Reserve, though some strong corporate earnings provided a reason to buy.
Optimism about earnings was boosted by Exxon Mobil Corp , one of the largest U.S. companies by market cap, which reported adjusted third-quarter earnings that beat expectations, sending shares 1.1 percent higher to $89.78.
Expedia also advanced following its results, topping the S&P 500 percentage gainers, while Facebook Inc fluctuated between steep gains and losses.
The Fed said Wednesday it had a weaker growth outlook for the U.S. economy, though it held steady with its stimulus program, which has fueled the S&P's 23 percent surge this year. That rally has come amid weaker-than-expected economic data and an earnings season marked by weak revenue.
"Nobody was surprised by the lack of action by the Fed, but there was a lack of clarity that was disappointing," said Rex Macey, who helps oversee $20 billion as chief investment officer at Wilmington Trust in Atlanta, Georgia.
"There is reason for caution at these levels, but nobody seems to be euphoric, so I don't think people need to get too defensive at this point."
The Dow Jones industrial average was down 48.61 points, or 0.31 percent, at 15,570.15. The Standard & Poor's 500 Index was down 4.95 points, or 0.28 percent, at 1,758.36. The Nasdaq Composite Index was down 15.18 points, or 0.39 percent, at 3,915.44.
The Dow has gained 2.9 percent in October, while the S&P has added 5 percent and the Nasdaq is up 3.7 percent.
Data on Thursday showed jobless claims fell slightly less than expected in the latest week, dropping 10,000 to 340,000. The Chicago Purchasing Manager's Index came in at 65.9, far ahead of expectations for a reading of 55.
While investors have been concerned by weak data pointing to slowing economic growth, strong data has also been viewed as a reason to sell, given that the Fed has said it would begin to slow its stimulus when economic growth meets its targets.
Facebook reported strong growth in its mobile advertising business late on Wednesday, though it said it didn't plan to boost the frequency of ads shown to users. Trading was volatile, with shares soaring during the premarket session but then turning sharply negative. They last traded at $48.38, down 1.3 percent.
Expedia jumped 18 percent to $59.98 a day after reporting third-quarter earnings that beat expectations, while Starbucks Corp fell 1.7 percent to $79.44 in the wake of a disappointing outlook.
Of 313 companies in the S&P 500 that reported earnings through Wednesday morning, 68.4 percent topped Wall Street expectations, above the 63 percent beat rate since 1994 and the 66 percent rate for the past four quarters, according to Thomson Reuters data. Only 53.7 percent of companies have topped revenue expectations, well below the 61 percent average since 2002.