PHILADELPHIA US Airways Group Inc. said in a Securities and Exchange Commission filing this week that a multibillion-dollar runway and terminal expansion at Philadelphia International Airport could harm its finances and business operations and force it to shift flights elsewhere.

The airline, which operates its largest hub in Charlotte, spoke out after the city of Philadelphia demanded that airlines sign a 15-year lease agreeing to pay for the runway.

In a 159-page regulatory filing, US Airways said that the expansion over the next 13 years would "result in huge cost increases for airlines serving Philadelphia" and that "expenditures have already begun."

US Airways transports nearly 70 percent of the Philadelphia airport's passengers.

"If we are unable to operate profitably from Philadelphia, we may need to significantly reduce our business at Philadelphia, or move that business to another of our hubs," US Airways said in its filing Wednesday.

"Our business, financial condition, and results of operations could be harmed by an increase in airport rates and fees charged by Philadelphia International Airport in connection with, and following, the airport expansion."

US Airways, backed by other airlines, first announced its opposition in January to a new runway along the Delaware River on 212 acres now owned and operated by United Parcel Service as an air-freight facility.

At the time, US Airways said it did not oppose the entire expansion but rather the proposed runway, which airlines contend would not greatly alleviate delays. That's because Philadelphia's airspace - which is shared with New York - is so congested. Nor would a new runway necessarily attract more international service, airlines said.

The city contends the runway is important to reduce chronic delays, especially in inclement weather, and to accommodate future growth. The expansion also would create thousands of temporary construction jobs.

US Airways' hub in Charlotte is its largest, with 595 daily flights. But Philadelphia, an international hub with 429 daily flights, generates more revenue.

Philadelphia city officials have estimated the total expansion cost at $6.4 billion. Airlines - which would foot much of the bill in rates and charges for debt service on airport revenue bonds - say it could cost $10.5 billion.

While no city tax dollars would be used, the Federal Aviation Administration permits a $4.50 passenger facility charge on each departing traveler to defray costs of airport improvement projects.

Mark Gale, the Philadelphia airport's chief executive, said, "We believe that we share common interests in finding an acceptable solution for all parties."