* Q3 adj operating profit 6.1 bln SEK vs forecast 6.6 bln * Q3 order intake 33 bln SEK vs forecast 31.1 bln * Shares fall 4% (Adds analyst, detail, updates shares) STOCKHOLM, Oct 21 (Reuters) - Atlas Copco missed third-quarter earnings forecasts on Thursday as supply chain challenges hampered its ability to capitalise on strong demand, knocking its shares. The Swedish company, which makes compressors, vacuum pumps and industrial tools, also said it expected near-term demand to weaken from the “very high level” in the quarter. Atlas has been helped by rising demand from chipmakers amid a global shortage of semiconductors, which are used in everyday products ranging from cars to computers. In the third quarter, it said a strong order increase for vacuum equipment to the semiconductor industry had been offset by slower order intake for other products. Shares in Atlas - down 2.3% ahead of the results - extended losses and were down 4.4% at 1129 GMT, having gained around 30% this year. “Revenue was hit by supply chain constraints – clearly more so than we and consensus had expected – and this impacted the profitability realised,” JP Morgan analysts said. “We would expect consensus to come down slightly for 2021 on the back of the Q3 earnings miss but the order strength, and the revenues still to be delivered, to support upgrades for 2022.” Order intake at Atlas, which competes with U.S. Ingersoll Rand and Germany’s Pfeiffer Vacuum among others, rose 36% year-on-year in the third quarter to 33.0 billion Swedish crowns. That topped analysts’ average forecast of 31.15 billion crowns in a Refinitiv poll. Adjusted operating profit was 6.11 billion crowns ($711 million), up from 5.02 billion a year earlier but missing the 6.62 billion mean forecast. “We have seen continued sequential order growth in some customer segments, but the overall order volumes for the Group did not increase compared to the previous quarter,” Chief Executive Mats Rahmstrom said in a statement. $1 = 8.5895 Swedish crowns Reporting by Helena Soderpalm Editing by Niklas Pollard and Mark Potter