* S&P 500, Nasdaq break six-day winning streak
* Apple announces seven-for-one stock split
* AT&T falls after results, but Boeing rallies
* Amgen drags biotech lower, but Gilead gains
* Dow off 0.1 pct; S&P 500 down 0.2 pct; Nasdaq off 0.8 pct (Adds Apple results, split)
By Chuck Mikolajczak
NEW YORK, April 23 (Reuters) - U.S. stocks dipped on Wednesday to snap a six-session winning streak as gains in Boeing and Gilead were offset by slides in AT&T and the wider biotech sector.
AT&T Inc fell 3.8 percent to $34.92 a day after the Dow component reported earnings that beat expectations, offset by weak service revenue growth. Verizon Communications shed 1 percent to $47.43 while the S&P telecom sector index dropped 2.2 percent, easily making it the session's worst-performing sector.
Biotech shares pulled the Nasdaq lower. Amgen Inc slid 5 percent to $113.32, a day after earnings missed forecasts. The Nasdaq biotech index fell 1.5 percent and NYSEArca biotech index lost 1.6 percent.
"You've got some big numbers coming out from companies that have already been pretty volatile in the Nasdaq, and there is some caution against the potential for shortfalls that could restart Nasdaq on the way down," said Rick Meckler, president of LibertyView Capital Management in Jersey City, New Jersey.
"This is traditionally not going to be a particularly strong time for earnings reports, and it's easy to take less inspiring numbers and say this market is overvalued or pass them by and say this is a seasonally low point. So it really is more about investors' own view of how high a multiple they are willing to pay."
There were bright spots within biotech. Gilead Sciences Inc rose 1.4 percent to $73.86 and Illumina Inc gained 3.9 percent to $153.69 after the companies posted results late Tuesday.
Boeing Co reported first-quarter revenue that beat expectations and lifted its core earnings forecast to reflect a tax settlement gain, sending its stock up 2.4 percent to $130.63 and giving the biggest boost to the Dow.
The Dow Jones industrial average fell 12.72 points or 0.08 percent, to end at 16,501.65. The S&P 500 lost 4.16 points or 0.22 percent, to 1,875.39. The Nasdaq Composite dropped 34.491 points or 0.83 percent, to 4,126.967.
After the closing bell, Apple Inc jumped 7.3 percent to $563 after the iPhone maker reported quarterly results, approved a seven-for-one stock split and expanded its share-buyback authorization by $30 billion.
In another big move after the close, Facebook Inc gained 4.8 percent to $64.30. Its mobile advertising business continued to accelerate in the first three months of the year, helping the social networking company top Wall Street's revenue target.
Better-than-expected earnings have buoyed Wall Street lately, though companies have largely been beating reduced forecasts. Profits are seen rising 1.6 percent this quarter, down from the 6.5 percent growth rate estimated at the start of the year, according to Thomson Reuters data.
Of the 141 companies in the S&P 500 that had posted results through Wednesday morning, 65.2 percent have topped expectations, above the long-term average of 63 percent. On the revenue side, 53.6 percent have exceeded forecasts, below the 61 percent long-term average.
Procter & Gamble Co's earnings topped forecasts but sales were flat. The stock slipped 0.3 percent to $80.36.
New home sales tumbled more than expected to an eight-month low in March. The PHLX housing sector index fell 1.1 percent, with D.R. Horton Inc off 2.2 percent at $21.35.
Volume was light, with about 5.67 billion shares traded on U.S. exchanges, well below the 6.65 billion average so far this month, according to BATS Global Markets.
Declining stocks outnumbered advancing ones on the NYSE by 1,566 to 1,482, while on the Nasdaq, decliners beat advancers by 1,775 to 819. (Editing by Nick Zieminski and Jan Paschal)