US STOCKS-Wall Street edges lower ahead of first presidential debate

* First U.S. presidential debate due to start at 9 p.m. EDT

* Democratic sweep modestly positive for S&P 500 profits - GS

* Consumer confidence rebounds in September

* Dow off 0.47%, S&P 500 down 0.28%, Nasdaq flat (Adds comment; updates prices)

By Devik Jain and Shreyashi Sanyal

Sept 29 (Reuters) - U.S. stocks inched lower in choppy trading on Tuesday after substantial gains a day earlier, with investors shifting their focus to the first presidential debate later in the day.

Eight of the 11 major S&P 500 sectors were lower, with energy stocks and financials leading declines, as they gave back some of their gains from the previous session.

President Donald Trump and Democratic challenger Joe Biden will lock horns in their first 90-minute televised debate in Cleveland, with the election now just five weeks away. Polls show Biden leading Trump nationally and in a number of key battleground states.

With Trump declining to guarantee he will accept the result on Nov. 3, speculation around the election has helped push up volatility on Wall Street, with analysts warning of more to come in the final weeks of the campaign.

"The markets will stay choppy between now and the end of the year, especially with all the uncertainty surrounding the election," said Eric Marshall, portfolio manager at Hodges Capital in Dallas.

"Today is really just some profit taking on the heels of a strong broadening out market rally that people were somewhat surprised by on Monday."

Goldman Sachs analysts said a victory for Biden in the election, along with the Democratic party controlling the Senate and the House of Representatives, would be slightly beneficial to profits for S&P 500 firms through 2024.

Among sectors, a stronger "green energy" push under a Biden administration could support alternative energy stocks, while a Trump victory could spell additional relief for companies that benefited from the president's corporate tax cuts.

"The market has its eyes set on the debate ... a potential change in tax plan could really have a significant impact on the stock market," said Thomas Hayes, chairman at Great Hill Capital LLC in New York.

While all three main indexes are on track for their first monthly decline since the coronavirus-driven selloff in February and March, the S&P 500 is still on course to rack up its two best back-to-back quarters since 2009.

The tech-heavy Nasdaq is on track for its biggest two-quarter jump since the dotcom crash in 2000.

Data showed U.S. consumer confidence rebounded more than expected in September as households' views of the labor market improved.

At 11:27 a.m. ET, the Dow Jones Industrial Average was down 129.28 points, or 0.47%, at 27,454.78, the S&P 500 was down 9.35 points, or 0.28%, at 3,342.25. The Nasdaq Composite was up 5.18 points, or 0.05%, at 11,122.71.

Among stocks, Sorrento Therapeutics jumped 12.4%, while Fitbit Inc gained 6.4% after Reuters reported Google was poised to win EU approval for its $2.1 billion acquisition of the fitness tracker maker.

Declining issues outnumbered advancers for a 1.86-to-1 ratio on the NYSE and for a 1.19-to-1 ratio on the Nasdaq.

The S&P index recorded six new 52-week highs and no new low, while the Nasdaq recorded 51 new highs and 23 new lows. (Reporting by Devik Jain and Shreyashi Sanyal in Bengaluru; Editing by Arun Koyyur, Patrick Graham and Anil D'Silva,)