FORT WORTH -- About 110 workers, mostly aircraft assemblers, were laid off at Lockheed Martin Aeronautics in west Fort Worth last week as a result of budgetary pressures in the defense industry, the company confirmed on Wednesday.Employees received notice of the layoffs in November, Lockheed spokesman Ken Ross said."The big thing is that we're going through a changing environment,"' he said. "We're responding to what is happening in the industry ... we want to make sure we remain competitive."Ross said the layoffs are not related to sequestration, the looming budget cuts that are possible if Congress cannot work out a budget deal in the next two months.He said he could not speculate about more layoffs, which he said are part of the "ebb and flow" of workers in the plant."Our intent is to keep the factory as full as possible ... but we can't speculate as to what's happening in the future," he said.Those affected by the layoffs worked on different production lines at the factory, Ross said. The decision about which employees to lay off were determined by union contracts.Speculation about defense industry cuts was widespread Wednesday during a meeting of the American Institute of Aeronautics and Astronautics at the Gaylord Texan Resort in Grapevine.At one panel discussion, a top official for Lockheed's F-35 joint strike fighter program said he believes the long-term, cost-effectiveness of the aircraft will continue to be a primary selling point despite well-documented delays and cost overruns.It is difficult to estimate "real costs" for the F-35 program, said Tom Burbage, Lockheed's executive vice president and general manager, F-35 JSF Program Integration. The program can't be measured by cost estimates that were used to quantify legacy programs, he said.Ultimately, he said, the F-35 will be less expensive to maintain than legacy aircraft "because of its simplicity,'' he told a room of more than 50 aviation officials and contractors.As the nation's biggest defense program, the F-35 is seen as a target for budget cutting in coming years. But for now, the program should not have to cut back on production and jobs thanks to two recent contracts.Last month, Lockheed received a Pentagon contract guaranteeing a final installment of about $127.7 million for the fifth production lot of F-35 fighters. And then just before the year's end, Lockheed and the Pentagon agreed to contracts for a sixth lot of 31 additional F-35 jets.About 6,000 of Lockheed's 14,200 workers at the west-side complex are directly involved in F-35 development, engineering and production, and many other jobs at the plant are tied to the program.Plans call for Lockheed to build more than 2,400 F-35s for the Air Force, Navy and Marines at a cost now estimated at $395.7 billion. But some wonder if that will be reduced if defense spending falls.