(Updates with market close)

* Main indexes on track for fourth straight weekly loss

* US deploying more troops to Middle East

By Noel Randewich and Johann M Cherian

March 20 (Reuters) - Wall Street ended sharply lower on

Friday, with losses in heavyweights Nvidia ( NVDA ) and Microsoft ( MSFT ), as the

U.S.-Israeli war against Iran entered its fourth week, deepening

worries about inflation and the potential for higher interest

rates.

The conflict in the Middle East showed no signs of easing. The

U.S. military was deploying a large amphibious assault ship with

thousands of additional Marines and sailors to the Middle East,

while Iran's new supreme leader hailed Iran's "unity" and

"resistance."

"The market is finally settling into the idea that this may

go on longer than initially expected, and I think that's why

markets are selling off. This conflict may go on not for just a

few weeks, but maybe beyond several months," said Jake

Dollarhide, CEO of Longbow Asset Management in Tulsa, Oklahoma.

MAGNIFICENT SEVEN COMPANIES FALL

Wall Street's most valuable companies declined, with Nvidia ( NVDA )

, Alphabet, Tesla, Meta Platforms ( META )

and Microsoft ( MSFT ) all losing ground.

U.S. Treasuries fell for a third session, in step with a broader

selloff in UK and European government bonds, as the Middle East

conflict kept oil prices elevated and reinforced inflation

worries.

U.S. rate futures show the Fed is more likely to raise

interest rates than cut them by the end of 2026, according to

CME's FedWatch tool.

"We just have a classic environment that is pushing rates

up and it's driven by higher inflation expectations, which

relate back to the oil price. And the fact that we're heading

into the fourth week of the war suggests that that stress is not

going away anytime soon," said Padhraic Garvey, head of global

rates and debt strategy at ING in New York.

According to preliminary data, the S&P 500 lost 99.01

points, or 1.49%, to end at 6,508.32 points, while the Nasdaq

Composite lost 436.98 points, or 1.98%, to 21,653.71.

The Dow Jones Industrial Average fell 422.32 points, or

0.92%, to 45,599.11.

Friday marks the once-in-a-quarter simultaneous expiry of

derivatives contracts tied to stocks, index options and futures,

also known as "triple witching," which can boost trading volume

and aggravate volatility.

All three main indexes were heading for their fourth

straight week of losses and were below their 200-day moving

averages, underscoring the recent deterioration of sentiment on

Wall Street.

Super Micro Computer ( SMCI ) tumbled after three people

associated with the artificial intelligence server maker were

charged with smuggling at least $2.5 billion of AI technology to

China. Rival Dell advanced.