US STOCKS-Wall St set to open lower as Greece concerns weigh

* Merkel and Hollande to meet this afternoon

* Greece owes $3.5 bln bond payment to ECB on July 20

* Aetna (NYSE: AET - news) falls after Humana (NYSE: HUM - news) deal

* Futures down: Dow 152 pts, S&P 16.25 pts, Nasdaq 34.5 pts (Adds details, comment, updates prices)

By Tanya Agrawal

July 6 (Reuters) - U.S. stocks were set to open lower on Monday after Greece rejected debt bailout terms, throwing the future of the country's euro zone membership into further doubt.

World markets (Xetra: 4WM.DE - news) fell, but less sharply than expected and analysts attributed the relatively muted reaction to expectations the European Central Bank would act to limit any damage.

A new bailout deal is needed for Greece to meet a July 20 deadline to repay $3.9 billion of bonds to the ECB.

The ECB's governing council began a conference call at 1000 GMT (6 a.m. ET) Monday to decide how long to keep Greek banks afloat. German Chancellor Angela Merkel and French President Francois Hollande will meet in Paris in the afternoon.

Greece's finance minister quit and Prime Minister Alexis Tsipras said his government was ready to return immediately to negotiations with creditors in a bid to open shuttered banks.

"I think what we are seeing now is that initial concerns were overblown," said Adam Sarhan, chief executive of Sarhan Capital (Other OTC: CGHC - news) in New York.

"Cooler heads are prevailing and now Tsipras can go to the creditors and have meaningful conversations. It also helps that the Greek finance minister is out because these negotiations can be very personality driven."

S&P 500 e-minis were down 16.25 points, or 0.79 percent, with 360,262 contracts traded at 8:49 a.m. ET. Nasdaq 100 e-minis were down 34.5 points, or 0.78 percent, on volume of 56,134 contracts. Dow e-minis were down 152 points, or 0.86 percent, with 40,390 contracts changing hands.

Data due on Monday is expected to show that the pace of growth in the U.S. services sector slowed in June from the previous month. The Institute for Supply Management's services index data is expected at 10 a.m. ET.

U.S. stocks closed slightly lower on Thursday ahead of the long holiday weekend and as investors digested mixed jobs data which dampened the economic outlook.

Some analysts say the combination of the Greek crisis and tepid employment data puts off a September rate hike by the Federal Reserve, which has said it will raise rates only when it sees a sustained economic recovery.

Health insurer Humana's shares rose 2.1 percent to $191.45 in premarket trading after bigger rival Aetna said on Friday it would buy the company for about $37 billion. Aetna fell 5.7 percent at $118.31.

Chipotle Mexican Grill (NYSE: CMG - news) fell 1.9 percent to $598 after Barron's said the stock has lost some of its luster recently and unless growth revives at the company, the stock could see a 15 percent to 20 percent plunge.

Weight Watchers soared 26.4 percent to $5.17 after the New York Post reported an activist hedge fund was in talks with potential partners about making a takeover offer for the company. The hedge fund and a partner "would like to offer perhaps double" Thursday's closing price, the report said. (http://bit.ly/1gjfCLt) (Editing by Savio D'Souza)