* Boeing union ratifies contract extension * Weekly jobless claims seen dropping in latest week * Futures down: Dow 11 pts, S&P 1.4 pts, Nasdaq 2.5 pts *By Ryan Vlastelica NEW YORK, Dec 8 U.S. stock index futures dipped on Thursday after three straight winning sessions as investors bet leaders at a euro zone summit will come up with a solution to the region's debt crisis. * The European Central Bank is expected to cut interest rates and unveil a new package of bank aid later Thursday. Market participants also looked for any hints the ECB will intensify its bond buying for the region's struggling peripheral economies.* Despite choppy trade, Wall Street has risen for three straight days on optimism European leaders would agree on a decisive plan to fight the crisis at Friday's EU summit. If the meeting disappoints, stocks may give up gains of about 9 percent, reached since Nov. 25. European stocks were little changed in light volume early Thursday. * S&P 500 futures fell 1.4 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 11 points, and Nasdaq 100 futures sank 2.5 points. * Late Wednesday, Standard & Poor's warned it could cut the credit ratings of the European Union and large area banks if a mass downgrade of euro zone countries materializes. The rating agency has said it may downgrade nearly all 17 euro zone countries if no solution emerges to solve the crisis. * Boeing Co's biggest labor union ratified a four-year contract extension late Wednesday, ensuring a new version its 737 narrowbody plane will be built in Washington state and likely ending a dispute with the National Labor Relations Board. * Weekly jobless claims are scheduled for release at 8:30 a.m. EST (1330 GMT) and are seen falling to 395,000 from 402,000 in the previous week. * Brown-Forman Corp and Pall Corp are scheduled to report quarterly results later in the day. * Costco Wholesale Corp reported first-quarter earnings and revenue that rose from the prior year. * McGraw-Hill Cos Inc launched a $500 million share repurchase program and said it will cut about 550 jobs from its textbook unit as it splits into two companies. * Hopes for a euro zone solution inspired enough buying to push U.S. stocks to a third day of gains on Wednesday in light trading.