* Yellen to speak at 1:00 p.m. ET
* Fed Vice Chairman Fischer set to speak at 12:30 p.m ET
* Snap Inc jumps on NBCUniversal's investment
* Indexes down: Dow 0.23 pct, S&P 0.23 pct, Nasdaq 0.24 pct (Adds details, comments, updates prices)
By Sweta Singh
March 3 (Reuters) - The S&P 500 and the Dow were set for their first back-to-back losses since late-January on Friday, as investors preferred to wait and watch Federal Reserve Chair Janet Yellen's speech for a steer on the chances of an interest rate hike this month.
Yellen could support a rising sentiment among policymakers for an increase in rates amid data pointing to an improving U.S. economy. She is set to speak at 1:00 p.m. ET (1800 GMT).
Also scheduled to speak is Fed Vice Chairman Stanley Fischer at 12:30 p.m. ET.
Traders have priced in a 75 percent chance of a rate hike when the Fed's policy-setting body meets on March 14-15. The odds stood at roughly 30 percent at the start of the week, according to Thomson Reuters data.
Investors are also assessing their positions following a strong rally on Wednesday, after President Donald Trump's pro-growth speech to Congress and a rise in bank stocks sparked a record day on Wall Street.
"I think we are at a position where we have the ability to move up a little bit higher (on rates)," said Paul Springmeyer, investment managing director at the Private Client Reserve at U.S. Bank in Minneapolis, Minnesota.
"But the difficulty is that we have a lot of other levers that are currently in flux, from a policy standpoint, and their potential impact on the equity markets."
The S&P 500 is already up 6.3 percent so far this year, compared with the 9.5 percent it gained in 2016, triggering worries over valuation.
At 11:02 a.m. ET (1602 GMT), the Dow Jones Industrial Average was down 44.89 points, or 0.21 percent, at 20,958.08, the S&P 500 was down 5.63 points, or 0.23 percent, at 2,376.29 and the Nasdaq Composite was down 14.29 points, or 0.24 percent, at 5,846.93.
Nine of the 11 major S&P sectors were lower, with high-dividend yielding utilities and real estate the biggest losers.
Financials, which benefit from higher rates, rose 0.39 percent, while a rise in oil prices propped up the energy sector.
Costco was the top drag on the S&P and the Nasdaq, falling 4 percent after its quarterly sales and profit missed analysts' expectations.
Snap Inc jumped 19 percent - a day after its much-awaited debut - after media company NBCUniversal said it had invested $500 million in the Snapchat parent.
Declining issues outnumbered advancers on the NYSE by 1,568 to 1,162. On the Nasdaq, 1,549 issues fell and 1,064 advanced.
The S&P 500 index showed two new 52-week highs and three new lows, while the Nasdaq recorded 31 new highs and 25 new lows. (Reporting by Sweta Singh and Yashaswini Swamynathan in Bengaluru; Editing by Sriraj Kalluvila)