American Airlines confirmed yesterday that it will move its headquarters and 1,000 employes from New York City to Dallas next year.

Albert V. Casey, president of the company, which is the nation's second largest domestic carrier, said the move was occasioned by changing route systems.

He called New York "a fine place in which to conduct business" and said "we will miss the many benefits and advantages that are unique both from a corporate and a personal standpoint."

American said it would retain in New York its Eastern Division headquarters, a metropolitan sales and service office, and all the airline's flight operations, airport services and maintenance units.

Rumors of the move, which would have a negative impact on New York City's economy, had elicited criticism from Mayor Edward Koch.

Koch said he was "distressed" by the firm's decision, but noted that there is a net increase of jobs in the city. "People always will be leaving," he said.

American is said to be looking to Dallas as a possible "hub" for expanding its Southwest route system.

New York City and state officials, who have fought to keep the company here, contend that other issues are involved, including the number of Texans on the company's board of directors.

The Cities of Dallas and Fort Worth offered American a $125 million municipal bond packages to finance the move and agreed to pay for 325 acres of land south of the airport. In addition, they agreed to build the headquarters and pay for an $18.5 million flight reservations center.

Meanwhile, an Eastern Airlines vice president said the proposed Pan American World Airways National Airlines merger could result in both National and Eastern moving out of Miami - possibly to New York.

Morton Ehrlick, Eastern's senior vice president for planning, said in Miami that if the merger is approved, the new airline probably would move its corporate base to New York.

In addition, he said, the National-Pan Am merger could force Eastern to seek a merger of its own with a stronger airline, and that could result in Eastern moving its corporate headquarters to another city.

Meanwhile, Georgia Pacific Corp. said it will relocate its national headquarters to downtown Atlanta from Portland, Ore.

The company previously had said it intended to move its headquarters but did not give a specific site.

The company said it is moving its national headquarters to the south-east U.S. because 75 percent of its business now is in the eastern part of the nation, and it said its major manufacturing growth in recent years has been in the South.