At the core of the X is a mall with fast-food restaurants, delis, bookstores and other retail shops, each contractually obligated to charge no more than prices at shops owned by these merchants outside of the airport. (See box.)

The airport also features a new $190 million, 7.5-mile expressway. At the parking lot, an enclosed moving walkway whisks passengers to the three-story "landside" terminal, with a 60-foot ceiling, arched skylights and a large mobile by Alexander Calder.

The 20th-busiest airport in the nation, Pittsburgh had 17 million passengers last year, more than 60 percent of them connecting passengers, and by 2003 is projected by the Federal Aviation Administration to have about 30 million passengers.

Like USAir's gleaming two-month-old $200 million terminal at La Guardia Airport in New York, the terminal here is a showcase and a proclamation of the carrier's intention to compete with the four biggest United States carriers, American, United, Delta and Northwest.

"AIRPORTS now understand that if passengers have a choice they will avoid going to or through airports that require long walks or are otherwise inconvenient," said Paul P. Bollinger, the senior vice president of the North American chapter of the Airports Association Council International. "Corporate travelers especially will tell their travel departments to avoid airports x or y."

But the new Pittsburgh airport is a costly showcase, for which USAir will pay more than $1 billion during its 30-year lease. USAir management initially hesitated to make such a costly, long-term commitment, said P. J. Boyle, deputy director of the Department of Aviation for Allegheny County, which owns the airport. It consented , he said, partly because of studies showing that the design would save so much in fuel costs.

Opposition to the new airport was relatively muted because it was constructed on the site of the old airport, built 40 years ago, and because the county had the foresight in the late 1960's to begin buying additional land -- enough for a second X-shaped terminal and an additional runway. But other communities have been roiled by contention. Chicago, for example, recently abandoned plans for a $10.8 billion airport at Lake Calumet, Ill., which had been beset by opposition from airlines that considered it unnecessary and expensive and protests from environmentalists and citizens who would have been displaced from their homes. And controversy continues over Denver's $3 billion airport scheduled to open next October. Denver International has been opposed by the Air Transport Association (the airlines' trade organization) and has drawn criticism as too costly from J. C. Pope, the president of United Airlines, which will be the airport's biggest tenant.