SILVER SPRING, Md. — Shortly after Elaine D. Harmon died in April at 95, her family found a letter in a fireproof box with explicit instructions: She wanted her ashes placed at Arlington National Cemetery.

“Even if there are no ashes left, I would like an empty urn placed at Arlington,’’ wrote Harmon, who had been part of a 1,000-women unit during World War II that transported military planes and bombers, and trained men to fly them.

But 10 months later, Harmon has not had a funeral, memorial service, or burial. A large black box of her ashes sits on a shelf above some blouses and sweaters in her daughter’s bedroom closet in a condominium in this Washington suburb.

Harmon’s family has delayed laying her to rest because the Army, which oversees Arlington National Cemetery, says her wartime unit, the WASPs — shorthand for Women Airforce Service Pilots — was not technically part of the military.

Thus, the Army ruled, her ashes cannot be placed in a columbarium there. (The Army also argues that the cemetery — where more than 400,000 veterans, their spouses and others are buried — is running out of space for graves and urns.)

Some members of Congress and veterans are outraged by the Army’s decision, saying it is a gross contradiction.

According to Army rules for the cemetery, had Harmon been married to a veteran already laid to rest at Arlington, her request would be approved, even if she had never served in a military unit. And several foreigners are buried in Arlington, including a German prisoner of war from World War II who died in US custody.

“Think of the irony that at the same time the Pentagon is opening up all missions to men and women in the military they are closing the door to the women who were pioneers,’’ said Representative Martha McSally, Republican of Arizona, referring to Defense Secretary Ashton Carter’s decision last year to open combat roles to women.

McSally, who was the Air Force’s first female fighter pilot to fly in combat, has introduced legislation that would allow the WASPs to be buried at Arlington. She said only about100 women from the unit were still alive, and that just two had requested they be laid to rest at the cemetery.

Support has built for the legislation, which has more than 10 cosponsors. On Thursday, the House Committee on Veterans’ Affairs sent the bill to the House floor.

“If you’re not going to do the right thing, we’re going to make it happen,’’ McSally said.

The Army said a legal review last year concluded that a technicality in legislation passed in 1977 prevented the WASPs from being buried at Arlington.

The bill designated the women as active duty for the purposes of Department of Veterans Affairs benefits. But that legislation did not give them status with the armed services, and so did not confer the right to be buried at Arlington.