Fed Chairman Jerome Powell is expected later on Wednesday to reaffirm that easy monetary policy will remain in place for a prolonged period and dismiss any suggestions of tapering bond purchases.
U.S. President Joe Biden will also address a joint session of Congress, where he may make additional comments about infrastructure and stimulus spending.
These developments would normally be a positive for stocks, but analysts say so much economic optimism is already priced into the equity market that it is difficult to buy stocks further from current levels.
"We expect the Fed's tone on the economy to be more positive than at the March FOMC meeting, reflecting the ongoing pickup in the data, but we don't expect any substantive new signal yet on tapering," analysts at TD Securities wrote in a research note.
"While we do not expect much price action due to the Fed decision, Biden's remarks could continue to suggest more incoming supply, bear steepening the (Treasury yield) curve."
The Dow Jones Industrial Average rose 0.01%, but the S&P 500 lost 0.02%, and the Nasdaq Composite dropped 0.34% as investors digested a mixed bag of earnings from Tesla Inc, 3M Co, Microsoft Corp, and Google-parent Alphabet overnight.
Some investors were also reluctant to move before earnings from heavyweights Apple Inc, Facebook Inc, and Amazon.com Inc due later this week.
An improving U.S. economy, rising coronavirus vaccination rates, and expectations for big fiscal spending are causing more investors to question when the Fed will start slowing its bond purchases and how much inflation policymakers will tolerate.
Breakeven rates on 10-year Treasury Inflation-Protected Securities, a measure of expected annual inflation for the coming decade, rose to 2.41%, the highest since 2013.
Yields on benchmark 10-year Treasuries reached a two-week high of 1.6430%.
The dollar edged up slightly against the yen and the British pound, but trading is expected to be subdued until Powell speaks after the Fed meeting.
The Australian dollar was knocked lower after disappointing data on consumer prices.
In the cryptocurrency market, Ether pulled back slightly from an all-time high above $2,700 reached after Bloomberg reported that the European Investment Bank plans to sell a two-year digital bond worth 100 million euros ($120.80 million) on the ethereum blockchain network.
Rival cryptocurrency Bitcoin edged lower to $55,618.
In commodities, Brent crude futures fell 0.03% to $66.40 a barrel while U.S. West Texas Intermediate crude lost 0.03% to $62.92 per barrel due to worries about energy demand.
Benchmark copper fell from a decade high of $9,965 a tonne hit on Tuesday due to concerns about softening demand in China, the world's top consumer of the metal.
Gold, which is often seen as a hedge against inflation, fell 0.28% to $1,771.70 in cautious trade ahead of the Fed meeting. ($1 = 0.8278 euros)
(Reporting by Stanley White; Editing by Sam Holmes) ((firstname.lastname@example.org; +81 (0)3 4563 2799; twitter.com/stanleywhite1 ;))