* Fed suggests preparing to do more to help economy
* Homebuilders up after rise in August housing starts
* Indexes up: Dow 0.5 pct, S&P 0.3 pct, Nasdaq 0.2 pct
* For up-to-the-minute market news see [
] (Updates with Fed comments, changes byline)By Ryan Vlastelica
NEW YORK, Sept 21 (Reuters) - U.S. stocks turned positive in volatile afternoon trading on Tuesday after the Federal Reserve said it stood ready to provide additional support to bolster a modest economic recovery.
While the central bank made no shift in monetary policy at the end of a one-day meeting, it opened the door wider to pumping more money into the economy. For details, see [
]"This keeps the status quo and was exactly what the market was looking for," said Steven Baffico, senior managing director at Claymore Securities Inc in Lisle, Illinois. "We've been getting some some encouraging data and stabilizing numbers, so they were very careful to telegraph their message."
After the Fed's August meeting, the U.S. central bank issued a bleak assessment of the economy and the S&P 500 tumbled more 4 percent over the next four days. Investors are hoping that improved economic data since then will mean a more upbeat outlook.
"Anything that would be dramatic by the Fed one way or the other would be unsettling, and the market is looking for some stability to move higher," said Ed Crotty, chief investment officer at Davidson Investment Advisors in Great Falls, Montana.
The Dow Jones industrial average <
> was up 54.04 points, or 0.50 percent, at 10,807.66. The Standard & Poor's 500 Index <.SPX> was up 3.10 points, or 0.27 percent, at 1,145.81. The Nasdaq Composite Index < > was up 4.79 points, or 0.20 percent, at 2,360.62.In Monday's session, the S&P 500 <.SPX> broke through a key technical range to close at a four-month high. The index has gained about 9 percent so far this month, but some analysts are unconvinced by Monday's breakout above 1,130, the upper end of a range that has persisted since June.
Sectors that had rallied recently, including technology and materials shares, gave back some gains on Tuesday. Dow component Microsoft Corp <MSFT.O> fell 0.6 percent to $25.27 while Alcoa Inc <AA.N> lost 1.8 percent to $11.18.
U.S. housing starts increased in August to their highest level in four months, while permits for future construction rose, suggesting the embattled housing market was starting to stabilize. [
]The Dow Jones home construction index <.DJUSHB> added 0.8 percent, and homebuilder D.R. Horton Inc <DHI.N> rose 0.9 percent at $11.14.
"It was very encouraging to see how strong the number was, but much of the strength was in multifamily homes, and that tends to be a volatile measure," Crotty said. "We want to see a trend of positive numbers before we become more bullish on the sector."
Airline shares rose, with the ARCA airline index <.XAL> adding 2 percent and rising to a 34-month high. A trade group forecast global airlines will likely post sharply higher 2010 profits. [
](Reporting by Ryan Vlastelica; Editing by Kenneth Barry)