* Amazon tumbles, Microsoft climbs after earnings
* New home sales climb to six-year high
* Indexes: Dow up 0.65 pct, S&P off 0.6 pct, Nasdaq up 0.49 pct (Updates to midday)
By Chuck Mikolajczak
NEW YORK, Oct 24 (Reuters) - U.S. stocks advanced on Friday, as earnings from Microsoft and Procter & Gamble and easing concerns over the possible spread of Ebola in the United States helped put the S&P on track to snap a four-week losing skid.
Microsoft was up 2 percent at $45.91, after it reported higher-than-expected quarterly revenue while keeping its profit margins largely intact.
Fellow Dow component Procter & Gamble gained 2.7 percent to $85.51 and was also one of the biggest boosts to the S&P 500, after the world's largest household products maker posted quarterly results and said it would split its Duracell battery business into a separate company.
But Amazon plunged 7.5 percent to $289.69 as the biggest drag on both the S&P 500 and Nasdaq 100 after the online retailer's sales projections for the crucial holiday quarter disappointed Wall Street and third-quarter results missed forecasts.
According to Thomson Reuters data through Friday morning, of 205 companies in the S&P 500 that have reported earnings, 69.8 percent have topped analyst's expectations, above the 63 percent rate since 1994 and the 67 percent rate for the past four quarters. On the revenue side, 59.8 percent have beaten expectations, slightly below the 61 percent rate since 2002 but above the 58 percent rate for the past four quarters.
The S&P 500 is up 3.9 percent for the week, putting the index on track for its best week since the start of 2013, boosted largely by solid corporate earnings reports. The benchmark index is down 2.5 percent from its record high set on Sept. 18 after slumping more than 7 percent as volatility has spiked.
Investors continued to monitor developments on the Ebola virus. A doctor who worked in West Africa with Ebola patients was in an isolation unit in New York City after testing positive for the virus, while the World Health Organization set out plans for speeding up development and deployment of experimental Ebola vaccines.
"The management of the Ebola virus has given the market some confidence that they can move forward and focus on what pricing is really predicated upon - earnings and data - and in both cases they have been very constructive," said Peter Kenny, chief market strategist at Clearpool Group in New York.
At 12:18 p.m. Eastern time the Dow Jones industrial average rose 107.6 points, or 0.65 percent, to 16,785.5, the S&P 500 gained 11.73 points, or 0.6 percent, to 1,962.55 and the Nasdaq Composite added 21.88 points, or 0.49 percent, to 4,474.67.
Sales of new U.S. single-family homes rose to a six-year high in September, up 0.2 percent to a seasonally adjusted annual rate of 467,000 units.
The largest percentage gainer on the S&P 500 was Edwards Lifesciences, which rose 12.0 percent, while the largest decliner was Amazon.
On the Nasdaq 100 the largest gainer was KLA-Tencor , which rose 7.3 percent, while the largest decliner was Amazon.
Advancing issues outnumbered declining ones on the NYSE by 1,782 to 1,164, for a 1.53-to-1 ratio on the upside; on the Nasdaq, 1,353 issues rose and 1,195 fell for a 1.13-to-1 ratio favoring advancers.
The benchmark S&P 500 index was posting 32 new 52-week highs and 2 new lows; the Nasdaq Composite was recording 40 new highs and 30 new lows. (Editing by James Dalgleish, Bernadette Baum and Chris Reese)