The six men and six women are also asking to be reinstated in the military. All were discharged after their sexual orientations became known to their to superiors. The plaintiffs represent all branches of the armed services except the Marines.
Lawyers for the Bush administration asked U.S. District Judge George A. O'Toole Jr. to dismiss the case, known as Cook vs. Rumsfeld, arguing that "courts should not second-guess congressional judgment."
The Boston judge did not rule immediately, and did not indicate when he would decide whether to accept or reject the government's request.
Nearly 10,000 members of the military have been dismissed since the policy was introduced.
"You cannot re-litigate questions that were reasonably reviewed by the legislative branch," said Assistant U.S. Atty. Mark Quinlivan. The military's ban on open homosexuality, he argued, helps to maintain cohesion in military units by "reducing sexual tensions and promoting personal privacy."
Six previous lawsuits challenging the "don 't ask, don 't tell " policy have been unsuccessful. Two others are pending, including a case called Log Cabin Republicans vs. Bush, filed last fall in Los Angeles.
But the Boston case is the first to base its arguments on Lawrence vs. Texas, a 2003 Supreme Court decision that struck down state laws against sodomy.
"Lawrence changed the landscape," said C. Dixon Osburn, executive director of the Servicemembers Legal Defense Network, which filed the case on behalf of the 12 gay and lesbian veterans.
Osburn said that 65,000 gays and lesbians were serving in the U.S. military. He said there were a million gay and lesbian veterans.
Dismissing gay and lesbian service members, he said, reduces military ranks "at a time when the military is not meeting its recruiting goals."
Megan Dresch, 22, was the only one of the plaintiffs to attend the Boston hearing. She joined the Army in 2001 and was discharged a year later after she told a superior officer she was a lesbian.
According to the Associated Press, Dresch said she was feeling "stressed" while serving with the Army's 230th Military Police Company in Germany. When she told her sergeant that she wanted to see a chaplain, he asked what the problem was, Dresch said. She said another member of the company interjected, and said the problem was that she was gay.