An announcement is expected to come in the next several days. Officials discussed the plan on the condition of anonymity because they were not authorized to publicly speak about internal Pentagon deliberations.
Pentagon press secretary George Little declined to comment. Other officials made it clear that there are still last-minute legal discussions going on to determine the details.
Officials said the military likely will require that some type of document be signed to designate the military member's partner as a legitimate recipient of the benefits. The same-sex partners are also expected to be issued some type of identification card that would give them access to the military installations and programs.
Panetta's decision comes as he nears the end of his tenure as Pentagon chief and on the heels of President Barack Obama's broad call for equal rights for gays during his inaugural speech.
"Our journey is not complete until our gay brothers and sisters are treated like anyone else under the law for if we are truly created equal, then surely the love we commit to one another must be equal as well," said Obama, who also has supported gay marriage.
Also, just days ago, a woman married to a female Army officer at Fort Bragg was invited to become a full member of the North Carolina base's officers' spouses club after initially being denied. The Marine Corps has also said that any spouses clubs operating on its bases must admit same-sex partners.
Last year, Rep. Adam Smith of Washington state, the top Democrat on the House Armed Services Committee, introduced legislation that would extend same-sex benefits to spouses of veterans and service members. He argued that with gays serving openly in the military, their spouses should receive the same benefits.
Under his measure, the Defense Department and Veterans Affairs Department would have to recognize any marriage that has been recognized by a state, the District of Columbia, commonwealths or territories. Nine states and the District of Columbia now allow gay and lesbian couples to marry.
"Building on the repeal of 'don't ask, don't tell,' this is another big step toward full equality in the military. No individual should be deprived of the benefits they have earned simply because of who they have married," Smith said Tuesday.
Advocacy groups called on Panetta to take substantive steps and grant full benefits that are available under the law.
"Considering DADT was repealed well over a year ago, our families have waited far too long for the Defense Department to extend benefits to same-sex military spouses," said Stephen Peters, president of the American Military Partner Association, which advocates for gay and lesbian military families. "No military family should suffer because of outdated regulations. For the sake of our families, we hope for substantive action and look forward to hearing from Secretary Panetta on exactly what benefits will be extended."
The repeal of the ban on gays serving openly in the military took effect in September 2011, and since then the Pentagon has been reviewing policies and procedures to see what military benefits can be opened to same sex partners without violating DOMA.
The Supreme Court is expected to rule on the constitutionality of DOMA in June, but advocacy groups have argued that there are a number of administrative steps the Pentagon could take to treat same-sex military couples more fairly.