* S&P 500, Nasdaq on six-day winning streak as of Tuesday
* Boeing rallies after results, outlook; P&G edges down
* Key earnings on tap; Apple, Facebook out after the close
* Futures down: Dow 14 pts, S&P 2.5 pts, Nasdaq 7.5 pts (Updates prices, adds details on Boeing, P&G results)
By Ryan Vlastelica
NEW YORK, April 23 (Reuters) - U.S. stock index futures pointed to a slightly lower open on Wednesday as the latest corporate earnings failed to inspire investors to keep pushing equities higher following six straight days of gains on both the S&P 500 and Nasdaq.
Equities have recently been boosted by corporate earnings, with a number of prominent names topping expectations, though companies have largely been beating reduced forecasts. According to Thomson Reuters data, profits are seen rising 1.1 percent this quarter, down from the 6.5 percent growth rate estimated at the start of the year.
* Boeing Co reported first-quarter revenue that beat expectations and lifted its core earnings forecast to reflect a tax settlement gain, sending shares up 2.7 percent to $131.05 in premarket trading. Fellow Dow component Procter & Gamble Co's earnings topped analyst forecasts, though shares edged 0.2 percent lower before the bell.
* Gilead Sciences Inc rose 3.8 percent to $75.60 in heavy premarket trading a day after the drugmaker reported a sharp profit increase, helped by sales of its hepatitis C drug. Gilead's results, like those of Netflix Inc , showed there was still room to grow in high-flying names that recently plunged on signs of excessive valuation.
* With 20 percent of the S&P 500 having reported results through Tuesday morning, 63 percent have topped earnings expectations, according to Thomson Reuters data, matching the long-term average. On the revenue side, 51 percent have exceeded forecasts, below the 61 percent long-term average.
* S&P 500 futures fell 2.5 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 dipped 14 points and Nasdaq 100 futures lost 7.5 points.
* Both the S&P 500 and Nasdaq closed out six straight days of gains on Tuesday. The S&P rose 3.5 percent over that period while the Nasdaq added 4 percent.
* In another positive sign for equities, the Dow Jones Transportation Average rose 0.6 percent on Tuesday to close at a record high, its first since April 2. However, trading volume was light, suggesting a lack of investor conviction behind the move.
* AT&T Inc late Tuesday raised its full-year revenue growth outlook, citing its acquisition of LEAP wireless in March and the popularity of a new handset pricing model that charges customers for devices separately from their wireless plans. Shares of the Dow component fell 2.2 percent to $35.50 in premarket trading.
* Dow Chemical Co rose 2.5 percent to $50.17 in premarket trading after the company reported better-than-expected quarterly earnings, helped by improved margins.
* More key reports are expected Wednesday, with Apple Inc and Facebook Inc scheduled for release after the market closes.
(Editing by Chizu Nomiyama and Nick Zieminski)