USAir Inc., the Arlington-based airline that had hoped to build itself into a major national and international carrier, yesterday announced it would dismiss 1,500 newly hired employees and shelve its latest plans for expansion.

In a late-afternoon announcement after stock markets had closed, USAir, the nation's seventh-largest airline, said "current economic projections" led it to fire workers hired in the last six months, resulting in the savings of unspecified millions of dollars.

Employees received their notices of the move immediately.

"They come across the board, in most departments, in most employee groups throughout the company and throughout the country," USAir spokesman Susan Young said of the dismissals.

She said she had "no further specifics" on where the firings took place, what kinds of jobs were affected or how much USAir would save.

Analysts said the move was severe but not unexpected as recession fears mount, fewer people fly and fuel costs remain sky-high because of the Persian Gulf crisis.

USAir already was smarting from rising expenses, including the costs of its merger with Piedmont Aviation Inc. in 1989. It posted a $75 million loss in the second quarter this year, its fourth straight quarterly loss.

"USAir was a company somewhat in trouble as it was, and {recent economic developments} only exacerbate their vulnerabilities. They are taking internal measures to control costs," said Kevin C. Murphy, an airline analyst with Morgan Stanley Co. in New York.

But USAir is not faring as badly as others right now, Murphy said.

"The dominos are in place in the airline industry," he said, "but there are half dozen other airlines that are going to fall over before USAir," which include cash-short companies including Eastern, Midway, TWA and Pan Am airlines.

The firings are USAir's second wave of job cuts in two weeks. Last week, it laid off 211 pilots; yesterday, the company said in a statement, "Additional reductions in personnel will be announced as determined."

USAir Group Inc., the airline's holding company, employed 55,200 workers as of Aug. 5, including 3,000 to 4,000 in the Washington area, said David H. Shipley, another company spokesman. By comparison, the company employed 48,500 workers as of August last year.

Yesterday's dismissals struck only new workers, categorized as "probationary employees," who had been hired since February in anticipation of previously undisclosed expansion plans, USAir officials said.

They said those plans -- which have not been revealed for competitive reasons -- have been postponed indefinitely because there isn't enough business to sustain them.

USAir, which completed a $1.6 billion takeover of Piedmont in 1989 and a $385 million buyout of Pacific Southwest Airlines in 1987, has grown rapidly under deregulation, adding new routes, planes and airports annually.

This summer, it announced new international flights to central Europe and more domestic flights.

Murphy said that as of July, USAir planned to purchase 187 new aircraft, more than any other airline outside industry leaders United Airlines, American Airlines and Delta Airlines.