WASHINGTON - Lieutenant-Colonel Martha McSally is the U.S. Air Force's highest ranking female combat pilot, having flown A-10 Warthog tank busters over Iraq, but if she wants to leave her air base in Saudi Arabia, she is not allowed to drive.

She also has to be dressed in a black abaya robe, be accompanied at all times by a man and sit in the back seat while her male subordinates drive her around.

The policy, which applies to her and 1,000 other U.S. female military personnel stationed in the country, was not dreamed up by Saudi Arabia's strict Islamic monarchy, but by the U.S. military.

After quietly lobbying the Pentagon for years to change the policy, Lt.-Col. McSally is suing to have it declared unconstitutional.

"It strikes right at the heart of our Constitution," said John Whitehead, president of the Rutherford Institute, a civil rights organization that came to fame by championing Paula Jones in her sexual harassment lawsuit against former president Bill Clinton and which now represents Lt.-Col. McSally.

"She's a Christian. By having to wear that abaya, she has to subvert her own religion.

"Her cause has been taken up by an unusual coalition of right-wing Republican congressmen and liberal feminists, who are lobbying the White House to have the policy changed.

So far, the Pentagon has not responded to the lawsuit, filed last month, but Lt.-Col. McSally's action is hugely embarrassing for the U.S. government.

The military's sensitivity to its position in Saudi Arabia has led it to impose policies on female troops that do not apply at U.S. bases in any other Islamic country. Other branches of the U.S. government in Saudi Arabia, such as the State Department, do not require their female employees to wear the abaya and not drive.

The female pilot is scathing about the policy.

"If it were in our national security to deploy to South Africa under apartheid, would we have found it acceptable or customary to segregate African-American soldiers from other soldiers," she recently asked a group of students at Washington's National Cathedral School. "I would hope not.

"When those customs and values conflict with ones that our Constitution is based on, and that women and men in uniform died for in the past, that is where you draw the line," she said.

Drawing the line could cost Lt.-Col. McSally dearly.

Until she went public she had been on a fast track to make general. But in the past six months she has received her first negative assessment from a senior officer, chiding her for not being a team player.

"She could have shut up and had a real nice career but she decided to stand up," said Mr. Whitehead. "She's the cream of the crop, but for some strange reason she's a second-class person in Saudi Arabia."