CHICAGO, April 22 (Reuters) - Shares of major U.S. air carriers fell on Monday as the latest attempt to raise fares and provide more revenue following the Sept. 11 attacks unraveled, analysts said. Shares in America West Airlines (AWA), the eighth largest U.S. carrier, led the decline in percentage terms by falling more than 15 percent, but the stocks of the top seven U.S. carriers all fell on fare-related jitters, one analyst said. The American Stock Exchange airline index (XAL) was off 3.7 percent on Monday, outpacing losses on the broader market. "There is a lot of confusion over fare activity," Deutsche Bank Securities airline analyst Susan Donofrio said. "A second broad-based fare increase was attempted, but given different management philosophies, it didn't stick." America West's shares fell one business day after its chief executive told analysts that large U.S. carriers slashed some fares out of Phoenix, America West's hub, in retaliation for America West's decision to cut business fares in March. America West shares were off 54 cents, or 10.55 percent, to $4.58 in late morning trade on the New York Stock Exchange. Shares of American Airlines' parent AMR Corp. (AMR) were off 65 cents, or 2.9 percent, at $21.75. Shares of UAL Corp. (UAL), parent of No. 2 U.S. carrier United Airlines, fell 37 cents, or 2.5 percent, to $14.63 and Northwest Airlines (NWAC) fell $1.12, or 5.6 percent, to $19.02. Last week, American Airlines, the world's largest carrier, raised leisure fares by $20 per round-trip ticket systemwide. Most other major U.S. carriers matched the increase on a widespread basis as the industry made a second attempt in as many weeks to generate more revenue. However, No. 4 U.S. carrier Northwest refused to match widespread increases and most carriers, including American Airlines, rolled back the increase over the weekend, Bestfares.com Chief Executive Tom Parsons said. Northwest also refused to go along with an increase led by Continental Airlines (CAL), the No. 5 U.S. carrier, two weeks ago. By Monday morning, only Delta Air Lines (DAL), the No. 3 U.S. carrier, still had the increase listed, Parsons said. ©2002 Reuters Limited.