US STOCKS-Wall Street treads water ahead of first presidential debate

* First 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 flat, S&P 500 up 0.13%, Nasdaq up 0.11% (Updates to open)

Sept 29 (Reuters) - Wall Street’s main indexes steadied on Tuesday after substantial gains a day earlier, with a positive reading on consumer confidence soothing nerves about the economy as attention turned to the first U.S. presidential debate.

The 11 major S&P 500 sectors were split down the middle in early trading with five falling and energy stocks and financials, which bounced strongly in the previous session, giving back most of their gains.

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.

“It’s end of the month, most of the rebalancing is in the rear-view mirror and the market has its eyes set on the debate,” said Thomas Hayes, chairman at Great Hill Capital LLC in New York.

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.

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.

“This is the most important thing to watch because the potential change in tax plan could really have a significant impact on the stock market,” Hayes said.

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.

Also on the radar were talks between U.S. House of Representatives Speaker Nancy Pelosi and White House Adviser Larry Kudlow on a coronavirus relief bill a day after Democratic lawmakers had unveiled a new, $2.2 trillion package.

By 10:28 a.m. ET, the Dow Jones Industrial Average was up 5.12 points, or 0.02%, at 27,589.18, and the S&P 500 was up 4.51 points, or 0.13%, at 3,356.11. The Nasdaq Composite was up 11.84 points, or 0.11%, at 11,129.36.

Among stocks, Sorrento Therapeutics jumped 8.5% while Fitbit Inc gained 6.5% after Reuters reported Google was poised to win EU approval for its $2.1 billion acquisition of the fitness tracker maker.

Declining issues marginally outnumbered advancers on the NYSE and the reverse on the Nasdaq.

The S&P index recorded six new 52-week highs and no new low, while the Nasdaq recorded 45 new highs and 13 new lows. (Reporting by Devik Jain and Shreyashi Sanyal in Bengaluru; Editing by Anil D’Silva, Arun Koyyur and Patrick Graham)