GM's shares slumped 8.9%, underscoring the uncertainty facing global automakers at a time of technological and economic disruption. Shares of rival Ford Motor Co fell 5.0%.

Nine of the 11 S&P indexes were lower, with industrials and energy both slipping, as data showed U.S. private payrolls increased far less than expected in July, likely constrained by shortages of workers and raw materials.

The blue-chip Dow, heavily weighted toward economically-sensitive stocks, also declined.

The technology-heavy Nasdaq bucked the trend after another report showed a measure of U.S. services industry activity jumped to a record high last month, suggesting a broader economic rebound was still on track.

"The ADP employment report this morning (is a) big miss ... has people really locked in on tomorrow's initial claims and then Friday's non-farm payrolls report," said Ross Mayfield, investment strategist at Baird in Louisville, Kentucky. "To me that's a big driver (of the market today)."

"Broadly, the continued evolution of COVID-19, the Delta variant over the recent weeks and months kind of re-rating of the growth outlook" has the market coming to terms with what it means for the reflation trade, and what it means to the bond market, Mayfield said.

After six straight month of gains, the benchmark S&P 500 has struggled to rise in August over concerns about the pace of growth as the economy rebounded from the depths of the COVID-19-driven recession, and fears of higher inflation overshadowed a stellar corporate earnings season.

Federal Reserve Vice Chair Richard Clarida said on Wednesday the central bank should be in the position to begin raising interest rates in 2023.

Still, tech and tech-adjacent stocks such as Netflix Inc and Facebook Inc, which tend to perform better when interest rates are lower, outperformed the broader market.

Focus now turns to the Labor Department's monthly jobs report on Friday.

The Dow Jones Industrial Average fell 323.73 points, or 0.92%, to 34,792.67, the S&P 500 lost 20.49 points, or 0.46%, to 4,402.66 and the Nasdaq Composite added 19.24 points, or 0.13%, to 14,780.53.

In earnings-related moves, BorgWarner Inc fell even as it beat profit expectations on strong consumer demand for new vehicles, while Kraft Heinz Co tumbled after warning of margin pressure from higher prices of ingredients.

Robinhood Markets Inc jumped 50.4% as interest from star fund manager Cathie Wood and small-time traders set up the stock for a fourth session of gains after its underwhelming market debut last week.

Volume on U.S. exchanges was 9.78 billion shares, compared with the 9.71 billion average for the full session over the last 20 trading days.

Declining issues outnumbered advancing ones on the NYSE by a 2.02-to-1 ratio; on Nasdaq, a 1.82-to-1 ratio favored decliners.

The S&P 500 posted 67 new 52-week highs and 3 new lows; the Nasdaq Composite recorded 93 new highs and 107 new lows.

(Reporting by Echo Wang; Additional reporting by Sagarika Jaisinghani, Sruthi Shankar and Shashank Nayar in Bengaluru; Editing by Arun Koyyur, Aditya Soni and Diane Craft)

By Echo Wang