The aeronautics unit of Lockheed Martin Corp, the Pentagon's No. 1 supplier by sales, said on Thursday that it plans to cut about 1,500 jobs to reduce costs in response to a flattening of U.S. defense spending.

The aeronautics unit, which produces the F-16 multi-role fighter jet, C-130 military transport aircraft and F-35 Joint Strike Fighter, said some salaried workers would be offered voluntary separations to minimize the number of involuntary layoffs that would occur.

In Washington, Senator John Cornyn of Texas, where Lockheed assembles the F-16, said the move illustrated a need to boost U.S. arms exports.

The Obama administration should end its blockade of Taiwan's request to purchase new F-16s, he said in a statement.

Taiwan has sought for years to buy 66 F-16C/D models, a sale opposed by China. It deems Taiwan a rogue province subject to unification with the mainland, by force if necessary.

If this administration's highest priority is to jump-start

our sluggish economy, it should work aggressively to ensure American companies are top contenders when friendly nations are assessing their defense equipment needs, said the Republican, who had held up the nomination of William Burns to be the second-ranking State Department official over what Cornyn regards as administration foot-dragging on new F-16s for Taiwan.

Lockheed said those eligible for voluntary layoffs would be informed in August, and an involuntary reduction would begin in mid-September, with the greatest impact from the cuts likely to be on workers in higher-level labor grades.

The world's biggest defense contractor has about 28,000 employees at aeronautics unit sites in Texas, Georgia and California and at six smaller U.S. locations. The job reductions will likely have the greatest impact at larger sites, the company said.

Bold and responsible action is necessary to meet customer expectations and reduce our costs, Ralph Heath, executive vice president for the aeronautics division, said in a statement.

Earlier this month, Lockheed's space systems unit said it planned to cut about 1,200 jobs out of that division's total U.S. workforce of about 16,000 by year's end.

Lockheed overall has about 126,000 workers worldwide.

(Reporting by Karen Jacobs and Jim Wolf; Editing by Gary Hill and Steve Orlofsky)