Negotiations aimed at preventing a walkout began Friday, and the carrier is threatening to shut down if a strike occurs. The talks are being supervised by Ernest DuBester, chairman of the National Mediation Board, which oversees labor disputes in the transportation industry. Negotiations are expected to continue until an agreement or the strike deadline — 12:01 a.m. EST Saturday — is reached.

President Clinton, who can legally block the walkout temporarily, also will be kept up to date on the proceedings. But officials said the administration has no plans currently to intervene while the mediation board does its work.

US Airways Executive Vice President Lawrence Nagin said, "We are singularly focused on reaching an agreement that is fair both to the flight attendants and to the company."

For its part, the Association of Flight Attendants sent a letter to US Airways investors last week in an attempt to build outside pressure on the airline.

"Rather than sit down and negotiate a fair contract with the flight attendants, US Airways is planning to hurt its employees, hurt its passengers and hurt its investors by shutting the airline down," said the letter, signed by Lynn Lenosky, president of the union's US Airways council.

About 10,000 US Airways flight attendants are working under a contract that expired at the end of 1996 and gave them their last pay raise, of 4 percent, at the beginning of that year.

The attendants are permitted to strike if no agreement is reached after a 30-day cooling-off period, which runs through Friday.

The union has said that if a strike does occur, attendants probably would not walk off the job en masse. Rather, they would target selected routes with impromptu walkouts that could surprise management and passengers.

The attendants have released a list of 49 routes that could be affected, including Washington-Boston, San Francisco-Philadelphia and New York and Orlando, Fla. Other major airlines serve all of the targeted routes, union officials said.

US Airways serves destinations in 38 states and the District of Columbia, as well as Canada, Europe, Mexico and the Caribbean.

US Airways would have the right to replace striking flight attendants, but unpredictable strike tactics could make that difficult. Airline officials say they will shut down all operations to avoid subjecting customers to disarray.

"US Airways simply cannot risk losing our customers' confidence," executives said in a Feb. 23 letter to employees. In case of a shutdown, the letter said, all workers — except flight attendants — would continue to be paid "for as long as is financially feasible." The Arlington, Va.-based airline has nearly 45,000 workers who could be furloughed.

US Airways is advising concerned customers to contact its ticket agents or their own travel agents. Nagin said the airline has planned to make alternative arrangements for passengers or compensate them on a case-by-case basis should problems arise.

The starting salary for US Airways attendants is $17,145 a year, while those at the top of the pay scale, with 14 years seniority, earn $36,918.

The attendants are resisting the airline's proposal to put them under a pay-and-benefits formula based on what its biggest competitors offer, plus 1 percent. Other unions representing US Airways workers have accepted the formula, which the company says must be applied across the board to be fair.

The flight attendants argue that management has not clearly spelled out how the formula would affect their pay and fear it could result in erosion of some benefits.

The nation's last airline shutdown because of a labor dispute was in 1998, when Northwest Airlines was grounded for two weeks, furloughing nearly 30,000 employees when its pilots struck.

In Northwest's case, Clinton stopped short of using his authority to stall a transportation strike for 60 days. Instead, he dispatched aides who ultimately coaxed the two sides back to the bargaining table. But in 1997, he ordered striking American Airlines pilots back to work almost instantly.