* Indexes down: Dow 0.48 pct, S&P 0.30 pct, Nasdaq 0.18 pct
* U.S. consumer prices and retail sales data due Wednesday
* Market rout not impacting economic outlook - Fed's Mester
* Under Armour climbs after posting upbeat revenue (Updates prices)
Feb 13 (Reuters) - U.S. stock indexes fell on Tuesday, undoing two strong days of gains that have settled some investor nerves ahead of a crucial reading on inflation.
Strong U.S. consumer price and retail sales data on Wednesday would fan fears over rising inflation and the pace of interest rate rises - the same worries that sparked a stock market rout after U.S. jobs data on Feb. 2.
Among the biggest movers were sportswear retailer Under Armour, up more than 15 percent on strong quarterly sales, and AmerisourceBergen, up 8 percent after the Wall Street Journal reported Walgreens was seeking to buy out the drug distributor.
"Investors are probably positioning with a bit of a risk-off mindset going into those two (economic data reports) tomorrow," said Matt Miskin, market strategist at John Hancock Investments.
"The core CPI estimate is a modest decrease from last month. But in the event that inflation does accelerate, that could lead volatility to continue as the Goldilocks environment may be under further pressure."
Cleveland Fed president Loretta Mester, a voting member in the central bank's rate-setting committee this year, said the recent stock market sell-off and jump in volatility will not damage the economy's overall strong prospects.
After a wildly volatile week that pushed the market into correction territory, U.S. stocks gained roughly 3 percent over Friday and Monday, their best two-day gain since June 2016.
By 12:34 p.m. ET (1734 GMT), the Dow Jones Industrial Average dipped half a percent to 24,484.07, the S&P 500 0.3 percent to 2,648.06 and the Nasdaq Composite just 12.38 points, or 0.2 percent, to 6,969.58.
Ten of the 11 major S&P indexes were lower, led by losses in the technology and healthcare indexes.
Benchmark U.S. 10-year Treasury yields were hovering at 2.8439 percent, shy of a four-year peak of 2.9020 percent hit on Monday.
The CBOE Volatility Index, a widely-followed measure of short-term stock volatility and seen as a contributing factor itself to the selloff, was last trading at 26.39 points, half the 50-point mark it touched last week.
The recent pullback wiped out all of January's gains for the benchmark S&P 500 and the blue-chip Dow, both now down more than 1 percent for the year. The tech-heavy Nasdaq is still clinging to a 0.87 percent gain for the year.
On a day of heavy trading in healthcare companies, Henry Schein and Patterson Companies fell 10 percent and 9 percent, respectively, after news of a U.S. Federal Trade Commission complaint against the dental supply firms.
Their losses were the biggest among healthcare distributors weighing up the possible ramifications of the AmerisourceBergen deal and a report of Amazon's push into the space.
Of the 70 percent of the S&P 500 companies that have reported earnings, nearly 78 percent of them topped profit expectations, according to Thomson Reuters data. That is above the 72 percent average beat-rate in the past four quarters.
Declining issues outnumbered advancers on the NYSE by 1,668 to 1,165. On the Nasdaq, 1,585 issues fell and 1,220 advanced. (Reporting by Sruthi Shankar in Bengaluru; Editing by Savio D'Souza)