* CPI, initial jobless claims data due
* Wal-Mart shares slip after earnings
* Futures off: Dow 21 pts, S&P 2.6 pts, Nasdaq 12.5 pts
By Chuck Mikolajczak
NEW YORK, Feb 21 (Reuters) - U.S. stock index futures were lower on Thursday, indicating the S&P 500 would extend declines after its biggest percentage drop in three months a day earlier, ahead of data on the labor and housing markets.
* A flurry of economic data is due, which investors will peruse for signs of economic progress, including weekly initial jobless claims at 8:30 a.m. ET (1330 GMT). Economists in a Reuters survey forecast a total of 355,000 new filings compared with 341,000 in the prior week.
* The January consumer price index is also due at 8:30 a.m., with estimates calling for a 0.1 percent increase compared with an unchanged reading in December. Excluding volatile food and energy items, CPI is expected to have risen 0.2 percent compared with a 0.1 percent increase in the previous month.
* At 8:58 a.m. (1358 GMT), information services company Markit releases U.S. flash Markit Manufacturing PMI for February. Economists in a Reuters survey forecast a reading of 55.5 compared with 55.8 in the final January release.
* Wal-Mart Stores Inc shed 1 percent to $68.50 in premarket trading after the world's largest retailer reported fourth-quarter earnings.
* The benchmark S&P index dropped 1.2 percent on Wednesday, its biggest decline since Nov. 14, after minutes from the U.S. Federal Reserve's most recent meeting suggested the central bank may slow or stop buying bonds sooner than expected.
* The Fed has used quantitative easing, or QE, since 2008 in a bid to stimulate the economy. The policy, which involves expanding the Fed's balance sheet to buy bonds, has been credited with pushing money into the stock market, and its withdrawal would remove a ballast for the markets.
* At 10:00 a.m. (1500 GMT), the National Association of Realtors releases existing home sales for January. Estimates forecast a 4.90 million annualized unit total in January versus 4.94 million annualized units in December.
* Also at 10:00 a.m., the Conference Board releases its report on January leading economic indicators. Economists in a Reuters survey forecast a 0.3 percent rise compared with a 0.5 percent increase in December.
* S&P 500 futures fell 2.6 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures lost 21 points, and Nasdaq 100 futures dropped 12.5 points.
* PC maker Hewlett-Packard Co and Intuit Inc are due to report quarterly results after the close.
* According to Thomson Reuters data through Wednesday morning, of the 405 companies in the S&P 500 that have reported results, 71 percent have exceeded analysts' expectations, compared with a 62 percent average since 1994 and 65 percent over the past four quarters.
* Fourth-quarter earnings for S&P 500 companies are estimated to have risen 5.7 percent, according to the data, above a 1.9 percent forecast at the start of the earnings season.
* European shares tumbled as weak economic data dealt a further blow to sentiment already hit by concerns the U.S. Federal Reserve may opt to withdraw the stimulus that fueled the recent equity rally earlier than expected.
* Asian shares declined, with Hong Kong shares down 1.7 percent while Shanghai shares slid 3 percent on worries about Chinese monetary policy tightening and the extension of property ownership curbs. Tokyo's Nikkei stock average .N225 ended down 1.4 percent, after closing on Wednesday at its highest since late September 2008.