(Adds final closing prices, volume data)

* Indexes up: Dow 0.55%, S&P 500 0.17%, Nasdaq 0.09%

* Nvidia ( NVDA ) falls after quarterly results

* Walmart ( WMT ) tumbles on conservative outlook with fuel

prices in the mix

* Quantum stocks jump on US investment in exchange for

stakes

By Sinéad Carew and Utkarsh Hathi

May 21 (Reuters) - Wall Street's three main indexes

closed slightly higher after Thursday's choppy session as oil

prices lost ground, with some officials citing progress in

U.S.-Iran peace talks even as both sides took opposing stances

over Tehran's uranium stockpile and control of the Strait of

Hormuz.

After spending the morning in the red, stocks clawed their

way back to gains in afternoon trading while oil prices shifted

from a rally to a decline.

While U.S. Secretary of State Marco Rubio told reporters there

had been "some good signs" in talks with Iran, he also said a

diplomatic deal between the U.S. and Iran would be unfeasible if

Tehran implemented a tolling system in the Strait of Hormuz,

which is a key conduit for oil transportation. A senior Iranian

source told Reuters that no deal has been reached with the U.S.,

but that gaps have been narrowed while Iran's uranium enrichment

and Tehran's control over the strait remained among the sticking

points.

Jason Pride, chief of investment strategy and research at

Glenmede, attributed volatility during Thursday's session to

investor reactions to speculation about geopolitics.

"We're sitting at high levels of valuation partly driven by

earnings," he said. "That overshadowed the concerns around Iran

but now earnings season is largely over. We're not going to

suddenly get any more good surprises out of earnings, which

means that market attention is now back to Iran. The market, on

a near-term basis, is going to be finding its way based on

rumors or actual announced deals regarding Iran."

The Dow Jones Industrial Average rose 276.31 points,

or 0.55%, to 50,285.66, marking a record closing high. The S&P

500 gained 12.75 points, or 0.17%, to 7,445.72 and the

Nasdaq Composite gained 22.74 points, or 0.09%, to

26,293.10.

"The silver lining is that from a market perspective, the

fragile ceasefire is still holding. It's positive there's still,

according to news reports, the possibility of an off-ramp. Oil

and market sentiment is very sensitive to every headline," said

Marc Dizard, chief investment officer at Huntington Wealth

Management. He added, however: "Nobody knows, except the inner

circle in Iran and in the U.S., how much progress is truly being

made."

Investors also reacted to the latest batch of earnings from big

U.S. companies. Walmart ( WMT ) shares tumbled 7.3% after the

largest global retailer forecast second-quarter profit below

estimates and maintained its annual targets. CFO John David

Rainey said consumers were feeling pressure from high fuel

prices and that if the "elevated cost environment persists, we'd

expect somewhat higher retail price inflation in Q2 and the

second half of the year."

Among the S&P 500's 11 major industry sectors, consumer

staples led losses with a 1.6% decline as it was

weighed down by Walmart ( WMT ) along with declines in some other

retailers that fell in sympathy, including Casey's General

Stores, down 3.3%, and Costco Wholesale ( COST ), which

finished down 2.2%.

Shares of Nvidia ( NVDA ), the world's most valuable company,

fell 1.8% as some investors took profits after the AI

heavyweight's upbeat second-quarter revenue forecast and $80

billion share-repurchase program. Its stock has gained sharply

so far this year but the pace of growth has slowed as investors

believe Nvidia ( NVDA ) will face tougher competition from chip rivals

including Intel ( INTC ) and Advanced Micro Devices ( AMD )

going forward. However, the Philadelphia Semiconductor Index

finished up 1.3% as investors viewed Nvidia's ( NVDA ) results as

a positive sign for the group.

In economic data, jobless claims fell last week, pointing to

continued labor market resilience, giving the U.S. Federal

Reserve room to keep its focus on inflation risks.

U.S. manufacturing activity rose to a four-year high in May as

businesses built inventories to guard against potential

shortages and rising prices tied to the Iran war.

Among other movers, IBM ( IBM ) rose 12.4% on news that the

Trump administration will fund a handful of quantum computing

companies, including a new IBM ( IBM ) venture, in exchange for stakes

in some of the firms.

GlobalFoundries ( GFS ) also climbed 14.9% while D-Wave

Quantum ( QBTS ) added 33.4%, Rigetti Computing ( RGTI ) jumped

30.6% and Infleqtion ( INFQ ) gained 31.5%.

Intuit's shares plunged 20% after the software maker

lowered the annual revenue forecast for its tax-filing software,

TurboTax, and said it would cut 17% of its full-time workforce.

Shares of tax preparer H&R Block ( HRB ) ended down 4.8%.

Advancing issues outnumbered decliners by a 1.51-to-1 ratio

on the NYSE, where there were 234 new highs and 106 new lows. On

the Nasdaq, 2,985 stocks rose and 1,798 fell as advancing issues

outnumbered decliners by a 1.66-to-1 ratio. The S&P 500

posted 11 new 52-week highs and four new lows while the Nasdaq

Composite recorded 96 new highs and 108 new lows.

On U.S. exchanges, 17.67 billion shares changed hands

compared with the 18.57 billion moving average for the last 20

sessions.