WASHINGTON – The Pentagon’s “don’t ask, don’t tell” policy is being challenged by 12 gays who have been separated from the military because of their homosexuality.

They planned to file a federal lawsuit today in Boston that would cite last year’s landmark Supreme Court ruling that overturned state laws making gay sex a crime as ground for overturning the policy.

Other courts have upheld the 11-year-old policy, but C. Dixon Osburn, executive director of Service members Legal Defense Network, which is advising the plaintiffs, said those decisions came prior to the 2003 Supreme Court ruling.

“We think the gay ban can no longer survive constitutionally,” he said.

Justin Peacock, a former Coast Guard boatswain’s mate from Knoxville, Tenn., who is among the plaintiffs in the planned U.S. District Court lawsuit, was kicked out of the service after someone reported he was seen holding hands with another man.

“I would love to rejoin, but even if I don’t get back in, at least I could say I tried to get the policy changed,” Mr. Peacock said.

Lieutenant Colonel Joe Richard, a Pentagon spokesman, said officials have not seen the lawsuit and therefore could not comment on it.

“Don’t ask, don’t tell,” put in place during the Clinton administration, allows gays and lesbians to serve in the military only if they keep quiet about their sexual orientation and abstain from homosexual activity. The Pentagon’s previous policy barred homosexuals from military service.

The Supreme Court ruled last year that state laws making homosexual sex a crime were unconstitutional. That overturned an earlier Supreme Court ruling that had upheld sodomy laws.

Two other lawsuits challenging the policy have been filed since the high court’s reversal.

One was brought in California by the Log Cabin Republicans, a political organization for gays. Mr. Osburn said that group could face a difficult fight because it was not bringing its suit on behalf of a specific injured party. He also noted a federal appeals court in California has upheld “don’t ask, don’t tell,” but the appellate court for Boston has not ruled on the issue.

The other suit was filed in the U.S. Court of Federal Claims, which generally deals with cases that involve money. That plaintiff, who was separated from the Army, is seeking to recover his pension and is challenging the ban in the process.

Mr. Osburn said the court might rule narrowly on the financial claim and not on the constitutionality of the gay members policy.