* Morgan Stanley second biggest drag on S&P 500
* Weight Watchers soars after Oprah takes stake
* China Q3 GDP data better than expected
* Indexes down: Dow 0.35 pct, S&P 0.37 pct, Nasdaq 0.23 pct (Updates to open)
By Abhiram Nandakumar
Oct 19 (Reuters) - U.S. stocks opened lower on Monday after a swathe of weak results led by Morgan Stanley and Halliburton.
Morgan Stanley's shares fell 6.2 percent to $31.83 after the bank's profit fell for the second straight quarter. The stock was the second-largest drag on the S&P 500 index.
The bank's results capped mostly downbeat quarterly results from major U.S. banks with struggling trading businesses.
Citigroup, JPMorgan, Wells Fargo slipped about half a percent. Goldman fell about 1 percent to $183.47 and was the biggest drag on the Dow Jones industrial average.
Halliburton fell 1.5 percent to $37.26 after reporting a bigger-than-expected 36 percent drop in quarterly revenue, hurt by weak drilling activity and pricing in North America.
"After three weeks of market gains, any disappointing earnings this morning could indicate that we could be in for some profit taking," said Peter Cardillo, chief market economist at Rockwell Global Capital in New York.
S&P 500 companies are expected to show a 3.9 percent fall in third-quarter profit, according to Thomson Reuters data.
Investors will continue scrutinizing company reports this week with several Dow components posting quarterly results, including Caterpillar, Boeing, Amazon and Coca-Cola.
At 9:35 a.m. ET (1335 GMT), the Dow was down 60.39 points, or 0.35 percent, at 17,155.58, the S&P 500 was down 7.56 points, or 0.37 percent, at 2,025.55 and the Nasdaq composite index was down 11.16 points, or 0.23 percent, at 4,875.53.
All 10 major S&P 500 sectors were down, with the energy sector leading the decline with a 1.2 percent fall.
Data on Monday showed China's economic growth slowed to 6.9 percent between July and September, but still ahead of the 6.8 percent forecast.
Reactions were mixed with most global markets rising as the data suggested that China may need more stimulus measures from Beijing though its economic health was not as bad as expected.
Brent crude oil prices fell 2.7 percent to $49.10 a barrel as worries mount about tepid demand from China and a global supply glut curbing Saudi exports.
IBM reports quarterly results after the close.
Data on U.S. homebuilder sentiment is due at 1000 ET (1400 GMT). The NAHB/Wells Fargo housing market index is expected to remain steady at 62 in October.
Federal Reserve of Richmond President Jeffrey Lacker, Chicago Fed President Charles Evans and Fed Board Governor Lael Brainard are scheduled to speak on Monday.
Weight Watchers surged nearly 70 percent to $11.40 after it said Oprah Winfrey will buy a 10 percent stake in the company and join the board.
Valeant Pharma's U.S.-listed shares fell 6.6 percent to $165.70 after the drugmaker reported a better-than-expected quarterly profit.
PMC-Sierra jumped nearly 14 percent to $11.66 after the chipmaker received a buyout offer from Microsemi, valuing the company at $2.4 billion.
Declining issues outnumbered advancing ones on the NYSE by 1,968 to 661. On the Nasdaq, 1,434 issues fell and 763 advanced.
The S&P 500 index showed one new 52-week high and two new lows, while the Nasdaq recorded nine new highs and seven new lows. (Reporting by Abhiram Nandakumar in Bengaluru; Editing by Don Sebastian)