* Indexes down: Dow 0.05%, S&P 500 0.07%, Nasdaq 0.27%

* Trump cancels US envoys' visit to Pakistan

* Qualcomm ( QCOM ) up 2.2% on report of OpenAI tie-up

* Microsoft ( MSFT ) down 1.2% after amended partnership with

OpenAI

(Updates after market open)

By Niket Nishant and Utkarsh Hathi

April 27 (Reuters) - Wall Street's main indexes were

marginally lower on Monday, ahead of a torrent of earnings this

week, as stalled peace talks between the U.S. and Iran kept

investors on edge.

Stocks have climbed to fresh highs in recent days on

earnings optimism even as back-and-forth headlines on the

U.S.-Iran war swayed sentiment.

The optimism will face a key test during the quarter's

busiest stretch of earnings this week. According to Raymond

James, companies accounting for roughly 44% of the S&P 500's

market capitalization are scheduled to report this week.

Of the 139 companies in the benchmark that reported as of

Friday, 81.3% surpassed earnings expectations, compared with the

prior four-quarter average of 78.1%, according to data from

LSEG.

However, some analysts have questioned how reliable the

results are as a guide to future performance, since they reflect

only one month of disruption linked to the Middle East war.

"While earnings are now demanding a lot of focus from

investors, certainly the constant drumbeat in the background is

the Iranian conflict," said Peter Andersen, founder at Andersen

Capital Management.

"There doesn't seem to be any progress on a resolution. Once

the earnings period is over, investors probably will start to

refocus on the Iranian conflict and what it means in the

long-term impact for the equity markets."

U.S. President Donald Trump canceled a visit by two U.S.

envoys to Pakistan, dealing a new blow to peace prospects.

At 10:10 a.m. ET, the Dow Jones Industrial Average

fell 25.18 points, or 0.05%, to 49,205.53, the S&P 500

lost 5.16 points, or 0.07%, to 7,159.92 and the Nasdaq

Composite lost 67.96 points, or 0.27%, to 24,762.66.

The trajectory of oil prices remains the biggest unknown, as

the crucial Strait of Hormuz is still closed. Brent crude

futures were trading about 2% higher on Monday and are

43% above pre-war levels.

Investors will also hear from Federal Reserve policymakers,

who will gather in Washington this week in what may be Jerome

Powell's last meeting as head of the U.S. central bank.

Republican Senator Thom Tillis said on Sunday he would allow

​the Senate confirmation of Fed chair nominee Kevin Warsh to go

forward, after the Department of Justice dropped an

investigation into Powell that Tillis said was a threat to the

central bank's independence.

"With those obstacles now removed, the path appears clearer

for Warsh's confirmation ahead of the next policy meeting (in

June)," said Jefferies' chief U.S. economist Thomas Simons.

A Reuters poll of economists last week showed that the Fed

is expected to wait at least six months before cutting interest

rates this year.

Four of the eleven main S&P sectors were in the red, with

the S&P 500 consumer discretionary leading losses with

a 0.9% drop.

Qualcomm ( QCOM ) was up 2.2% after an analyst said OpenAI

was working with the chip designer and Taiwan's MediaTek

to develop smartphone processors.

Microsoft ( MSFT ) declined 1.2% after OpenAI said on Monday

that the cloud computing provider will not have exclusive access

to its artificial intelligence models and products.

Domino's Pizza dropped 10.3% after the pizza chain

missed first-quarter sales estimates.

Nvidia ( NVDA ) gained 0.6% after jumping 4.3% in the

previous session. The company has reclaimed a market valuation

above $5 trillion.

Advancing issues outnumbered decliners by a 1.45-to-1 ratio

on the NYSE and by a 1.23-to-1 ratio on the Nasdaq.

The S&P 500 posted 13 new 52-week highs and five new

lows while the Nasdaq Composite recorded 85 new highs and 52 new

lows.

(Reporting by Niket Nishant and Utkarsh Hathi in Bengaluru;

Editing by Devika Syamnath)