* Symantec tumbles after CEO's firing
* Tensions between Russia and U.S. still in focus
* Nike shares fall after results
* Dow off 0.2 pct; S&P 500 down 0.3 pct; Nasdaq off 1 pct
(Updates to close)
NEW YORK, March 21 (Reuters) - U.S. stocks slipped on Friday, as investors booked profits in momentum names heading into the weekend, wiping out early gains that had pushed the S&P 500 to an intraday record high.
The S&P 500 lost momentum after hitting an all-time intraday high of 1,883.97, with biotechs among the primary decliners. Biogen Idec Inc, down 8.2 percent at $318.53, and Gilead Sciences Inc, down 4.6 percent at $72.07, were the two biggest drags on the S&P 500. The Nasdaq biotech index fell 4.4 percent.
U.S. lawmakers have asked Gilead to explain the $84,000 price tag of its new hepatitis C drug Sovaldi, which is encountering resistance from health insurers and state Medicaid programs.
"They've been selling them - the techs in particular, as well as the biotechs, even more particular there. Obviously, it's a momentum sector, and all the momentum names are getting smacked around," said Joe Saluzzi, co-manager of trading at Themis Trading in Chatham, New Jersey.
"When you see the momentum names coming out like they are now, that is telling you they are lightening up here."
Investors continued to monitor geopolitical issues after President Vladimir Putin signed laws completing Russia's annexation of Crimea. Russia's MICEX stock index fell 1 percent after a U.S. decision to slap sanctions on Putin's inner circle.
Nike Inc fell 5.1 percent to $75.21 and was the heaviest weight on the Dow after the maker of sports shoes and apparel said late Thursday that growing pressures from weak emerging market currencies would take a toll on profit.
The Dow Jones industrial average fell 28.28 points or 0.17 percent, to 16,302.77. The S&P 500 slipped 5.49 points or 0.29 percent, to 1,866.52. The Nasdaq Composite dropped 42.498 points or 0.98 percent, to close at 4,276.788.
For the week, the Dow rose 1.5 percent, the S&P 500 gained 1.4 percent and the Nasdaq advanced 0.7 percent.
First Solar continued its recent meteoric rise, climbing 4.1 percent to $73.37 on Friday, its sixth straight daily increase. The stock has jumped 38 percent over that period.
Symantec Corp tumbled 12.9 percent to $18.20 a day after it fired Chief Executive Officer Steve Bennett, the second time it has sacked its top executive in less than two years, raising concerns about its turnaround efforts.
Despite the market's recent strength, trading volume has been anemic on positive market days, suggesting limited conviction behind the move. However, volume received a boost on Friday as options expired alongside multiple index rebalances. Credit Suisse expected $14 billion in gross trading from the S&P 500 index rebalance, with another $6 billion from rebalancing in other indexes.
Volume of about 9.6 billion shares traded on U.S. exchanges, well above the 6.69 billion average so far this month, according to data from BATS Global Markets.
In earnings news, Tiffany & Co reported adjusted fourth-quarter earnings and gave a profit outlook that was below estimates. Tiffany's stock fell 0.5 percent to $90.73.
Darden Restaurants Inc reported results largely in line with expectations and affirmed its plan to divest its Red Lobster business. Darden's shares rose 2.8 percent to $50.66.
The U.S. Federal Reserve late Thursday said big U.S. banks have enough capital buffers to withstand a drastic economic downturn. The central bank said 29 of 30 major banks met the minimum hurdle in its annual health check.
The only bank to fall under the 5 percent requirement for top-tier capital was Zions Bancorp, which said it would resubmit a capital plan to the Fed. Shares of Zion fell 5.3 percent to $31.24.
Advancing stocks outnumbered declining ones on the New York Stock Exchange by 1,776 to 1,257. The opposite trend prevailed on the Nasdaq, where decliners beat advancers by 1,553 to 1,113.
(Editing by Chizu Nomiyama, Nick Zieminski and Jan Paschal)