Signaling a potentially tougher safety enforcement policy, federal aviation regulators proposed $9.2 million in civil penalties against US Airways and United Airlines for various maintenance lapses affecting more than 1,800 flights stretching back to early 2008.

The Federal Aviation Administration's new hard-nosed stance partly reflects heightened congressional and public concerns about maintenance slipups, according to industry and government officials. But Wednesday's announcement, these officials said, also may be a prelude to seeking potentially larger fines or penalties in pending enforcement cases targeting two other carriers that recently have been more prominently in the agency's crosshairs: American Airlines and Southwest Airlines.

The FAA proposed a $5.4 million penalty against the US Airways Group Inc. unit for allegedly operating eight aircraft between October 2008 and January 2009 that hadn't been properly inspected or otherwise failed to comply with government and airline safety procedures. UAL Corp.'s United unit was hit with a proposed $3.8 million penalty for flying a Boeing 737 jet for more than two months after mechanics left rags inside the oil system of one of its engines. Both carriers have 30 days to appeal.

The fines are among the largest ever proposed by the FAA.

A UAL spokeswoman said the carrier was "reviewing" the penalty.