* Initial jobless claims fall for fourth straight week
* Equity markets close at 1 p.m. in holiday-shortened session
* Indexes up: Dow 0.21 percent, S&P 0.13 pct, Nasdaq 0.2 pct (Updates to market open)
By Chuck Mikolajczak
NEW YORK, Dec 24 (Reuters) - U.S. stocks edged higher on Wednesday, extending a five-day winning streak that pushed the Dow and S&P 500 to new closing records and on the latest piece of economic data indicating the U.S. economy is strengthening.
Initial claims for state unemployment benefits dropped 9,000 to a seasonally adjusted 280,000, its fourth straight week of declines, and below the forecast of 290,000.
"Economic data has been consistently positive," said Peter Kenny, chief market strategist at Clearpool Group in New York.
"We are positioned well into the close of the year and we have all sorts of validation that the economy, the corporate earnings story and markets are on the most solid footing they have been on in quite some time."
The Dow closed above 18,000 for the first time ever on Tuesday and the S&P 500 ended at its 51st record of the year after an unexpectedly strong report on U.S. economic growth. The 51 new closing highs are the most since 1995 and fourth best in history.
Equity markets will operate on a shortened trading schedule Wednesday, closing at 1 p.m. EST (1800 GMT) ahead of the Christmas Day holiday on Thursday. Volume is expected to be light, which could exacerbate volatility.
The benchmark S&P index has risen 5.5 percent in its latest rally, the best 5-day run since December 2011, fueled by a commitment by the U.S. Federal Reserve last week to take a "patient" approach toward raising interest rates amid solid economic data.
The Dow Jones industrial average rose 38.42 points, or 0.21 percent, to 18,062.59, the S&P 500 gained 2.78 points, or 0.13 percent, to 2,084.95 and the Nasdaq Composite added 9.72 points, or 0.2 percent, to 4,775.15.
Adamas Pharmaceuticals Inc jumped 22.6 percent to $17.96 after the U.S. Food and Drug Administration approved a drug developed with Actavis Plc to treat dementia in Alzheimer's patients. Actavis shares rose 0.3 percent to $256.67.
U.S. surgical implant maker Stryker Corp is planning to make an offer for British medical device maker Smith & Nephew Plc that may come within weeks, Bloomberg reported, citing sources. U.S.-listed shares of Smith & Nephew were down 2.5 percent to $37.10 while Stryker edged up 0.2 percent to $96.63.
Advancing issues outnumbered declining ones on the NYSE by 1,429 to 1,232, for a 1.16-to-1 ratio on the upside. On the Nasdaq, 1,203 issues rose and 976 fell for a 1.23-to-1 ratio favoring advancers.
The benchmark S&P 500 index posted 59 new 52-week highs and 5 new lows. The Nasdaq Composite recorded 36 new highs and 9 new lows. (Editing by Chizu Nomiyama and Jeffrey Benkoe)