(For a Reuters live blog on U.S., UK and European stock markets, click LIVE/ or type LIVE/ in a news window.) * Declines in big tech-related firms pressure Nasdaq, S&P 500 * Walmart slides as tepid outlook overshadows upbeat Q4 sales * Facebook shares slip on news blackout move in Australia * Indexes down: Dow 0.87%, S&P 1.00%, Nasdaq 1.43% (Adds comments; Updates prices to early afternoon) Feb 18 (Reuters) - Wall Street’s main indexes fell on Thursday as investors resumed a shift out of big technology-related firms, while an unexpected rise in weekly jobless claims pointed to a fragile recovery in the labor market. Shares of Apple Inc, Microsoft Corp, Tesla Inc and Alphabet Inc were down between 1.1% and 2.5%, pressuring both the S&P 500 and the Nasdaq . Facebook Inc shares slipped 2.4% as Wall Street assessed the wider ramifications of its move to block all news content in Australia. A stronger-than-expected earnings season, progress in countrywide vaccination efforts and hopes of a $1.9 trillion dollar stimulus package helped U.S. stock indexes hit record highs at the beginning of the week. However, concerns over a potential rise in inflation have pushed investors to book profit on stocks with high valuation in the S&P 500 technology and communications services sectors, which have underpinned a 76% rise in the benchmark index since its March 2020 lows. “There was a lot of irrational exuberance built into things heading into the year ... then we started to enter an environment where risk actually became a factor once again and notably inflationary risk,” said Peter Essele, head of portfolio management at Commonwealth Financial Network in Boston. “Now it’s a question of whether the fundamentals are going to match the level of prices that currently exist in the market.” The Labor Department’s report showed initial claims for state unemployment benefits were 861,000 last week, compared with 848,000 in the prior week, partly due to potential claims related to the temporary closure of automobile plants due to a global semiconductor chip shortage. “It’s going to be some time and a choppy return to a normal employment environment. But, by and large, as vaccines begin to take hold as we get out from under the COVID overhang, you’re going to see a decline in unemployment,” Essele said. Only the defensive utilities sector was in positive territory, out of the 11 major S&P 500 sectors. Walmart Inc slid 5.5% after the world’s largest retailer missed quarterly profit estimates and predicted fiscal 2022 net sales to rise in low single digits. At 12:13 p.m. ET the Dow Jones Industrial Average was down 275.87 points, or 0.87%, at 31,337.15, the S&P 500 was down 39.18 points, or 1.00%, at 3,892.15 and the Nasdaq Composite was down 199.51 points, or 1.43%, at 13,765.99. Marriott International Inc was down 0.1% after reporting a quarterly loss as the hotel chain’s bookings declined due to pandemic-induced travel restrictions. Declining issues outnumbered advancers for a 3.21-to-1 ratio on the NYSE and for a 3.29-to-1 ratio on the Nasdaq. The S&P index recorded 12 new 52-week highs and no new low, while the Nasdaq recorded 74 new highs and 14 new lows. (Reporting by Devik Jain and Shreyashi Sanyal in Bengaluru; Editing by Saumyadeb Chakrabarty and Anil D’Silva)