NEW YORK, Sept 4 (Reuters) - Shares of Nvidia ( NVDA )

and other Big Tech stocks have helped power the markets run to

record highs this year. Their recent wobble is making investors

nervous.

A tumble in the chipmaker's shares shaved $279 billion off

Nvidia's ( NVDA ) market capitalization on Tuesday, the single largest

one-day decline in market value on record for a U.S. company.

The stock was rebounding on Wednesday, rising 1% in late morning

trading.

Whether the steep fall is due to investors becoming more

cautious towards the artificial intelligence trend that

supercharged market returns this year or worries over the health

of the U.S. economy, more trouble for Nvidia ( NVDA ) and other Big Tech

stocks would likely spell trouble for the broader markets.

Nvidia ( NVDA ) - along with Apple ( AAPL ), Microsoft ( MSFT ),

Amazon ( AMZN ) and Alphabet - currently make up more

than a quarter of the weight in the S&P 500 and over a third of

the Nasdaq 100. Nvidia ( NVDA ) alone had comprised 23% of the S&P

500's year-to-date total return of 19.5% as of the end of

August.

Further losses in their shares would likely hurt those

indexes, which hit record highs in July, unless stocks in other

sectors of the market pick up the slack.

"When you look at Nvidia ( NVDA ) as a market leader, it's not

holding up despite very strong profits," said Jason Teh, chief

investment officer of Vertium Asset Management in Sydney.

"There's an old saying - if the troops can't follow the

generals, it's a warning sign."

Nvidia's ( NVDA ) quarterly forecast last week failed to meet the

lofty expectations of investors even as second quarter revenue

and profit topped estimates.

"Those earnings last week were fine; they exceeded

expectations," said Steve Sosnick, market strategist at

Interactive Brokers. "But the magnitude of the beats is

shrinking quarter by quarter and that's not lost on investors."

Index funds that track the S&P 500, Nasdaq 100 and other

benchmarks also stand to suffer if Nvidia ( NVDA ) slides, because of the

stock's increasingly heavy weighting in these indexes. The

chipmaker has even more sway in more narrow indexes and exchange

traded funds that focus on technology and semiconductor shares.

Even with its recent slide, Nvidia ( NVDA ) shares have more than

doubled in 2024, as of Tuesday's close, and the stock remains

the best year-to-date performer in the S&P 500. Shares of the AI

heavyweight are up a whopping 800% since October 2022.

Nvidia's ( NVDA ) ascent has helped drive the valuation of the

broader S&P 500 technology sector higher, causing some concerns

about a bubble in tech stocks. But the sector's forward

price-to-earnings ratio remains well below levels reached in

2000, during the dot-com era.