* Yellen to speak on Friday, no new policy view expected
* Amazon to close Whole Foods deal Monday; Grocery shares fall
* Oil slips as U.S. refineries shut ahead of Harvey
* Dow down 0.13 pct, S&P 500 down 0.21 pct, Nasdaq down 0.11 pct (Updates to close, adds comments)
Aug 24 (Reuters) - U.S. stocks dipped on Thursday as political uncertainty in Washington kept investors cautious ahead of comments on monetary policy from central bankers gathered for their annual meeting in Jackson Hole, Wyoming.
Speeches by Federal Reserve Chair Janet Yellen and European Central Bank President Mario Draghi on Friday will be scrutinized for hints on the path of monetary policy, but neither of them is expected to give fresh guidance.
The focus on central bankers' views will be a departure from the past two weeks, when the stock market was roiled by concerns over geopolitics, mayhem in Washington, and President Donald Trump's controversial comments.
President Donald Trump picked a new fight with fellow Republicans whose support he needs to advance his policy agenda, saying congressional leaders could have avoided a "mess" over raising the U.S. debt ceiling if they had heeded his advice.
U.S. House of Representatives Speaker Paul Ryan later said Congress will pass legislation to raise the federal debt ceiling and lawmakers have a number of options for avoiding default.
"There are two stories that play out in Washington these days and to a degree it does impact the market - can the President have any success with the overall Washington agenda, whether it is the debt ceiling or tax reform - so far it seems like that is not going to be simple," said Phil Blancato, CEO of Ladenberg Thalmann Asset Management in New York.
"On the other side, there really is a necessity to see some tax reform to help the greater economy."
Recent economic data painted a mixed picture. The number of Americans filing for unemployment benefits rose less than expected last week, while home resales unexpectedly fell in July to their lowest monthly level of the year.
The Dow Jones Industrial Average fell 28.69 points, or 0.13 percent, to 21,783.4, the S&P 500 lost 5.07 points, or 0.21 percent, to 2,438.97 and the Nasdaq Composite dropped 7.08 points, or 0.11 percent, to 6,271.33.
Oil prices slipped amid concerns over demand. U.S. Gulf Coast refineries shut operations as Hurricane Harvey was forecast to turn into a major hurricane.
Consumer staples, down 1.3 percent, were the worst performing of the 11 major S&P sectors, led lower by a 9.5 drop in J.M. Smucker after its posted disappointing results and lowered its earnings forecast.
The group also lost ground after Amazon.com Inc said it plans to complete its $13.7 billion acquisition of Whole Foods Market Inc on Monday after winning antitrust approval from U.S. regulators. The announcement weighed on grocery store stocks such as Kroger Co, off 8.10 percent, and Wal-Mart Stores Inc, down 2.03 percent.
Dollar Tree advanced 5.6 as one of the best performers on the S&P 500 after the retailer's profit and comparable sales beat estimates.
Signet Jewelers surged 16.7 percent after the company issued results and said it would buy an online jeweler.
Advancing issues outnumbered declining ones on the NYSE by a 1.02-to-1 ratio; on Nasdaq, a 1.47-to-1 ratio favored advancers.
About 5.27 billion shares changed hands in U.S. exchanges, below the 6.08 billion daily average over the last 20 sessions. (Additional reporting by Chuck Mikolajczak and Sruthi Shankar in Bengaluru; Editing by Savio D'Souza and Nick Zieminski)