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Updates with afternoon trading levels

By Shashwat Chauhan and Kanchana Chakravarty

May 20 (Reuters) - Wall Street's main indexes fell on Tuesday, with the benchmark S&P 500 on track to end its six-day winning streak as investors awaited commentary from central bank officials to gauge the impact of U.S. tariffs on the Federal Reserve's policy path.

The Nasdaq Composite .IXIC was set to follow the benchmark index to record its first loss in three sessions, if declines held.

At least seven Fed officials including St. Louis Fed President Alberto Musalem are scheduled to speak through the day.

"With a market that has rallied so much in a pretty short amount of time on very little news that's substantial, it's just trying to digest it all and figure out what the next catalyst is," said Robert Pavlik, senior portfolio manager at Dakota Wealth.

U.S. stocks have had a solid month so far, with the S&P 500 now more than 17% higher than its April lows, when U.S. President Donald Trump's reciprocal tariffs roiled global markets.

A pause in the tariffs, a temporary trade truce between the U.S. and China and tame inflation data pushed equities higher, although the S&P 500 is still about 3% from its record highs.

Earlier in the week, Fed officials flagged the ramifications of the latest downgrade of the U.S. government's sovereign credit rating and uneasy market conditions.

Traders currently expect at least two 25-basis-point rate cuts from the U.S. Federal Reserve by the end of 2025, with the first one expected in September, according to data compiled by LSEG.

Retailer Home Depot HD.N pared earlier gains but was still slightly up after beating Wall Street estimates for first-quarter sales.

Most megacap and growth stocks fell, though Tesla TSLA.O was an outlier with a 1.8% rise after Elon Musk said at an economic forum in Qatar that he was still committed to being the company's CEO in five years.

Nine of the 11 S&P sub-sectors traded lower, with information technology .SPLRCT, which was down nearly 0.7%, being the worst hit.

At 11:49 a.m. ET, the Dow Jones Industrial Average .DJI fell 106.45 points, or 0.25%, to 42,684.69, the S&P 500 .SPX lost 20.96 points, or 0.35%, to 5,942.64, and the Nasdaq Composite .IXIC lost 77.89 points, or 0.40%, to 19,137.57.

The S&P 500 ended flat on Monday as investors assessed the implications of Moody's downgrading the U.S. sovereign credit rating to "Aa1" from a pristine "Aaa", citing the government's $36-trillion outstanding debt and interest.

Concerns around mounting U.S. debt remain in focus, with a vote on Trump's sweeping tax-cut bill in the House of Representatives expected this week.

Trump traveled to Capitol Hill on Tuesday to encourage Republican lawmakers to resolve their differences over the bill that encompasses much of his domestic agenda.

Preliminary readings of the May Purchasing Managers Index are due later in the week.

AI-favorite Nvidia NVDA.O is scheduled to report quarterly earnings on May 28.

Declining issues outnumbered advancers by a 1.08-to-1 ratio on the NYSE and by a 1.04-to-1 ratio on the Nasdaq.

The S&P 500 posted 15 new 52-week highs and no new lows, while the Nasdaq Composite recorded 45 new highs and 31 new lows.

(Reporting by Shashwat Chauhan and Kanchana Chakravarty in Bengaluru; Editing by Pooja Desai)

((Shashwat.Chauhan@thomsonreuters.com;))