* Netflix up after bell on 1st-qtr report, subscriber growth beat
* Merck rises on positive Keytruda drug data
* Optical stocks hit by report of ban on supplying ZTE
* Indexes up: Dow 0.87 pct, S&P 500 0.81 pct, Nasdaq 0.7 pct (Updates to close, adds commentary)
By Sinéad Carew
NEW YORK, April 16 (Reuters) - U.S. stocks closed higher on Monday, with the biggest boosts from technology and healthcare sectors as investors were optimistic about earnings season and appeared less worried about U.S.-led missile attacks in Syria.
The weekend's air strikes marked the biggest intervention yet by Western countries against Syrian President Bashar al-Assad and his ally Russia, which is facing further economic sanctions over its role in the conflict.
Stocks had ended lower on Friday on worries about Syria. But investors seemed less anxious about he potential for retaliation from Russia, an Assad ally, since there was none at the weekend.
"Geopolitical conditions calmed," said Tim Ghriskey, Chief Investment Strategist at Inverness Counsel in New York. "There's a lot of anticipation about very strong earnings growth in the quarter. That may be attracting traders and even longer-term investors back into the market."
Netflix shares gained around 7 percent after the market closed following its quarterly report. Its subscriber growth beat analyst expectations. It had ended the regular session down 1.2 percent.
S&P 500 companies are expected to report an 18.6 percent jump in first-quarter profit, on average, the biggest rise in seven years, according to Thomson Reuters data.
The Dow Jones Industrial Average rose 212.9 points, or 0.87 percent, to 24,573.04, the S&P 500 gained 21.54 points, or 0.81 percent, to 2,677.84 and the Nasdaq Composite added 49.64 points, or 0.7 percent, to 7,156.29.
The S&P 500's technology sector was the biggest boost to the benchmark on a weighted basis, with a 0.7-percent increase, followed by the healthcare index which rose 0.8 percent.
UnitedHealth provided the second-biggest boost to the S&P from a single stock a day ahead of its earnings report with a 2.7 percent gain. Microsoft Corp was the biggest positive contributor with a 1.2 percent gain, on a weighted basis.
Merck rose 2.6 percent after it presented positive data on its cancer drug Keytruda, also boosting the S&P healthcare index.
Shares of optical components makers, including those of Acacia Communications and Oclaro, took a beating after Reuters reported that the U.S. government was banning American companies from selling components to Chinese telecom equipment maker ZTE Corp. Acacia slumped almost 36 percent, compared with a 15.2-percent drop for Oclaro.
JB Hunt Transport Services jumped 6.2 percent after the trucking company's profit topped estimates.
Bank of America rose 0.44 percent after a bigger-than-expected increase in quarterly profit.
Advancing issues outnumbered declining ones on the NYSE by a 2.70-to-1 ratio; on Nasdaq, a 1.82-to-1 ratio favored advancers.
The S&P 500 posted 11 new 52-week highs and no new lows; the Nasdaq Composite recorded 68 new highs and 36 new lows.
On U.S. exchanges about 5.74 billion shares changed hands, in the lowest volume session so far this year. Monday's trading compared with the 7.03 billion average for the last 20 sessions. (Additional reporting by Sruthi Shankar in Bengaluru; Editing by Nick Zieminski and James Dalgleish)