American Airlines Inc., moving to expand its presence in the Southeast, announced yesterday that it will establish a major new north-south hub in Nashville that ultimately may schedule 135 flights a day to 60 nonstop destinations and create at least 1,350 new jobs.

American, the main unit of Fort Worth-based AMR Corp., has committed more than $115 million to build the new 15-gate terminal at Nashville Metropolitan Airport by summer 1987.

"This gives us a greater presence in the East Coast market," said Thomas G. Plaskett, American's senior vice president for marketing. Most of American's traffic now flows east to west through its two major hubs at Dallas-Fort Worth International Airport and Chicago's O'Hare International.

"This is an opportunity for growth for American," said Helane Becker, an airline industry analyst with Prudential Bache Securities. "They needed an East Coast hub."

American has been stepping up its service to the Southeast, and there had been speculation for months that the airline would open a new hub in the region. Nashville, which is a popular convention site and vacation center, was chosen primarily for its strategic geographic location, strong economy and balanced work force, Plaskett said.

With a 21 percent share of the Nashville market last year, American already is Nashville's largest carrier. The airline currently operates 15 flights daily from Nashville to 19 cities.

American's major competitors in the Nashville market last year included Delta and Republic, each with about 15 percent of the market, and Eastern and USAir, which each had 11 percent, according to airport spokesman Martha Bradley.

Wesley G. Kaldahl, American's senior vice president for airline planning, said the airline plans to spend an estimated $113 million to build a 104,000-square-foot, L-shaped concourse at the new terminal being built by Nashville Metropolitan Airport.

American first will expand its current facilities at the airport into a nine-gate "minihub" by next spring. The minihub, which will serve more than 20 cities with 50 to 60 flights a day, will cost between $1.5 million and $2 million, Kaldahl said.

American spokesman Al Becker said the airline originally planned to develop a hub in the West before developing one in the Southeast. However, American reversed its plan after it ran into obstacles at its chosen western site, Denver's Stapleton International Airport.

"The original plan called for developing Denver as a hub by 1987 and then coming back and establishing a hub in the East to handle north-south traffic flow," Becker said. "A complication arose when the City of Denver decided to develop a new airport. That can't be done by 1987, and it might be 1990 before it could be ready," said Becker, who added that the airline still plans to build a Denver hub in the future.