The Pentagon announced Monday that it would extend additional benefits to same-sex military couples, including access to base facilities and groups as well as joint assignments, the latest move by the Obama administration to heed calls from gays and lesbians pressing for change.

Activists hailed the move as a meaningful step toward full equality, which they say will remain elusive unless a 1996 federal law that defines marriage as a heterosexual union is repealed. The additional 20 benefits do not include health-care coverage for same-sex spouses or on-base housing privileges.

Defense officials said they are studying whether they may be able to extend certain housing benefits without violating the Defense of Marriage Act, which restricts the Pentagon from extending more than 100 benefits to same-sex couples.

“It is a matter of fundamental equality that we provide similar benefits to all those men and women in uniform who serve their country,” outgoing Defense Secretary Leon E. Panetta said in a statement.

He expressed regret that the 1996 DOMA law does not allow the Pentagon to do more, adding: “While it will not change during my tenure as secretary of defense, I foresee a time when the law will allow the department to grant full benefits to servicemembers and their dependents, irrespective of sexual orientation.”

The Pentagon estimates that about 5,600 active-duty and roughly 3,400 National Guard servicemembers have same-sex spouses. During a briefing on the additional benefits, a defense official who spoke to reporters on condition of anonymity said the cost of extending benefits access would be “negligible.” The Pentagon said it hopes to offer the additional benefits by Aug. 31.

The biggest lingering question is whether the department might be able to offer on-base housing to same-sex couples. The Pentagon decided not to do so for the time being because on-base housing is scarce and because legal experts worried that doing so could have contravened the “spirit” of the federal marriage law, a defense official told reporters.

The issue would be moot if the Supreme Court strikes down DOMA this summer.

Advocates of gay troops hailed the Pentagon move, saying it was evidence that President Obama was making good on his promise to push for greater equality under the law for gays and lesbians.

“Secretary Panetta’s decision today answers the call President Obama issued in his inaugural address to complete our nation’s journey toward equality, acknowledging the equal service and equal sacrifice of our gay and lesbian servicemembers and their families,” said Allyson Robinson, executive director of OutServe-SLDN, a group that has been pressing for an extension of benefits.

News last week about the impending announcement generated supportive statements from Capitol Hill and did not appear to draw significant criticism from groups that have in the past raised concerns about allowing openly gay people to serve in the armed forces.

On Monday, however, the ranking Republican on the Senate Armed Services Committee accused the president of “pushing his liberal social agenda through the Department of Defense.”

“We are on a slippery slope here,” said Sen. James M. Inhofe (R-Okla.). “Why would the DoD extend benefits to same-sex partners and then deny cohabitation heterosexual couples the same benefits?”

Rep. Adam Smith (D-Wash.), the ranking member of the House Armed Services Committee, applauded the announcement.

“Just as no individual should be forced to hide who they love to serve their country, no individual should be deprived of the benefits they have earned simply because of who they married,” he said in a statement.