US STOCKS-Futures flat after heated Trump-Biden debate

* Chaotic first U.S. presidential debate dulls mood

* U.S. private payrolls rise more than expected in Sept - ADP

* Mega-cap technology firms hit by antitrust news

* Futures: Dow up 0.01%, S&P up 0.04%, Nasdaq off 0.09% (Adds comments, updates prices)

Sept 30 (Reuters) - U.S. stock indexes were trading flat after falling more than 1% on Wednesday as a heated first presidential debate pointed to a tough race ahead, with investors also locking in gains on the last day of the third quarter.

Trading on Wall Street has become more volatile in the past few weeks on increasing doubts whether President Donald Trump would accept the election’s outcome if he lost.

In a chaotic and bad-tempered first debate, Trump and Democratic rival Joe Biden battled fiercely over Trump’s record on the coronavirus pandemic, healthcare and the economy.

“It is becoming more likely that we won’t have a clear-cut winner on the night of the election and could have a few weeks of contested period,” said Masahiko Loo, portfolio manager at AllianceBernstein in Tokyo.

Analysts said stock markets could also see quarter-end rebalancing of investor portfolios on Wednesday, as the previous session was marked by market participants booking profits after a strong start to the week.

Wall Street’s main indexes are headed for their first monthly declines since March, when lockdowns slammed the economy.

Despite the expected weakness in September, the S&P 500 was on course for its best two-quarter winning streak since 2009 and the Nasdaq since 2000.

At 9:11 a.m. ET, Dow e-minis were up 3 points, or 0.01%, S&P 500 e-minis were up 1.5 points, or 0.04% and Nasdaq 100 e-minis were down 10.25 points, or 0.09%.

Futures cut earlier losses after a report showed U.S. private employers stepped up hiring in September and separate figures showed the Chicago PMI reading jumped to 62.4, the highest level since December 2018.

Investors now await a more detailed jobs report from the Labor Department on Friday.

Mega-cap technology-related companies including Apple Inc , Alphabet, and Facebook fell in premarket trading, pressured by antitrust-related action from the United States, China and the European Union.

Moderna Inc rose 3.1% after researchers said its COVID-19 vaccine candidate produced virus-neutralizing antibodies in older adults at levels similar to those seen in younger adults in an early safety study.

Walt Disney Co fell 1.3% as it plans to lay off roughly 28,000 employees, mostly at its U.S. theme parks.

Micron Technology Inc slipped 3.6% after the chipmaker said it has not yet obtained new licenses needed to sell its memory chips to China’s Huawei Technologies Co Ltd , which would cut its sales over the next two quarters. (Reporting by Devik Jain and Shreyashi Sanyal in Bengaluru; Editing by Arun Koyyur)