Full benefits would require the repeal of the Defense of Marriage Act, a 1996 law that defined marriage as the union of a man and a woman. The Pentagon lifted the ban on openly gay men and lesbians serving in the armed forces, but it cannot recognize their marriages, even if they are legal in some states, because military personnel are federal employees covered by the marriage law.

The Supreme Court is expected to rule this summer on whether the law is constitutional.

“Additional benefits, such as health care and housing allowances, are by statute currently only available to spouses and therefore cannot be made available to same-sex domestic partners of service members under current law,” Defense Secretary Leon E. Panetta wrote in a letter released by the Pentagon.

“In the event that the Defense of Marriage Act is no longer applicable to the Department of Defense, it will be the policy of the department to construe the words ‘spouse’ and ‘marriage’ without regard to sexual orientation,” he added, “and married couples, irrespective of sexual orientation, and their dependents will be granted full military benefits.”

Criticism came immediately from Senator James M. Inhofe of Oklahoma, the ranking Republican on the Senate Armed Services Committee, who released a statement saying, “Once again, the president is eroding our military’s apolitical stance and forcing conformity onto the rest of society by pushing his liberal social agenda through the Department of Defense.” He said the decision “will increase costs and demand for limited resources that are currently available for military families, active and reserve forces, and retirees.”

Gay rights organizations broadly endorsed the announcement, but stressed that steps remained to assure that all service personnel were treated equally.