In computer science, women earned only 18.2 percent of degrees in 2010, down from nearly 28 percent a decade ago.

“You’re seeing women move up within corporations. You’re seeing a lot more mentoring inside companies,” said Karen Panetta, who teaches engineering at Tufts University and edits Women in Engineering magazine.

“But the number of women going into technical engineering fields is a real problem.”

Today, one in four female engineering graduates chooses a career in aerospace, a figure that has not changed in nearly a decade, said Carole Hedden, an editor at Aviation Week magazine and author of an annual report on industry employment.

At a recent women’s leadership forum sponsored by Lockheed, Hewson warned that the long-term trend of women entering aerospace and defense is no longer assured.

“Frankly, we can’t take it for granted,” she told more than 350 women at the event on November 8, a day before the company’s board elected her to succeed Bob Stevens as CEO of Lockheed, the Pentagon’s biggest supplier and the world’s largest arms maker. “Women are losing ground.”

RECRUITMENT AND RETENTION

Hewson, 58, knows how hard it can be to break through the glass ceiling. She took 18 different leadership posts at Lockheed and moved her family eight times to reach the top. Her promotion to CEO came abruptly this month, when Lockheed’s board fired its first choice, Christopher Kubasik, after he admitted to an improper relationship with a subordinate.

Hewson’s long journey explains why defense companies find it tough to retain female employees. As women reach their mid-30s, many switch fields or leave to raise families, especially if they don’t see clear advancement opportunities, said Panetta.