President Obama is calling for the repeal of the 1996 Defense of Marriage Act, which bans same-sex married couples from receiving the same federal benefits available to opposite-sex married couples.

White House spokesman Jay Carney said Tuesday that Mr. Obama was “proud to support the [repeal effort], which would take the DOMA off the books once and for all.”

The announcement came a day before the Senate Judiciary Committee is set to conduct hearings examining the Respect for Marriage Act, a legislative vehicle designed to overturn DOMA.

“This legislation would uphold the principle that the federal government should not deny gay and lesbian couples the same rights and legal protections as straight couples,” Mr. Carney said.

The repeal law would mandate that the 1,100 federal rights, privileges, and benefits currently available only to heterosexual married couples must be guaranteed to same-sex married couples as well.

The Obama administration announced in February that the president considered DOMA unconstitutional and that the Justice Department would no longer defend it against legal challenges. House Speaker John Boehner (R) of Ohio stepped into the void and hired counsel to defend the statute. Congressional Republicans have threatened to reduce Justice Department appropriations to pay for the effort.

Despite the president’s action, DOMA continues to enjoy significant support in Congress and among many Americans. “Congress rightly recognized that the lifelong, faithful union of a man and a woman is the fundamental building block of thriving societies,” Austin Nimocks of the Alliance Defense Fund, which supports DOMA, said in a statement. “The union between husband and wife benefits society – especially children – in unique and special ways that cannot be duplicated by any other relationship.”

[Editor's note: The original version of the article misspelled Austin Nimocks' last name.]

He added: “We should not abandon what Congress wisely did … to appease a very small group of activists.”

Earlier Tuesday, Sen. Dianne Feinstein (D) of California pledged to fight to the end for DOMA’s repeal and to extend full federal benefits to married couples nationwide regardless of their sexual orientation.

“This is not a cause we are going to drop. We are not fainthearts,” she said during a news conference at the National Press Club in Washington. “If we don’t succeed this session, we will try again next session.”

Senator Feinstein, a sponsor of the repeal effort, said the proposed law does not force individual states to recognize gay marriage. It would require only the federal government to treat same-sex married couples on equal terms with opposite-sex married couples in federal programs and benefits.

The Respect for Marriage Act would apply solely to federal benefits and federal employees. Individual states would still be free to ban gay marriage and restrict state benefits to heterosexual married couples, the senator said.

Six states and the District of Columbia recognize gay marriage. Those states are Connecticut, Iowa, Massachusetts, New Hampshire, Vermont, and New York.

Forty-one states ban same-sex marriage.

The DOMA repeal bill faces an uphill battle. Currently, 29 senators, including Feinstein, support the measure. Supporters include all 10 Democrats on the Senate Judiciary Committee.

In 1996, when Congress passed DOMA, 14 senators voted against the law. The federal marriage law defines marriage as a union between one man and one woman. The restriction is applied for purposes of federal benefits such as Social Security, tax filing status, and inheritance taxes. It also applies to the employment benefits of all federal workers.

Rick Jacobs, chairman of the gay rights group Courage Campaign, said the effort has made “huge progress,” though he declined to predict when the repeal law might pass. “There is a sea change occurring,” he said.

Also speaking at the National Press Club were three gay couples who described their struggles under the federal marriage law.

Beth Vorro and Beth Coderre have been together for 26 years. They live in Rhode Island and were married in 2004 in Massachusetts. Ms. Vorro is a lawyer for the federal government, and Ms. Coderre is a psychotherapist in private practice.

After their marriage, Vorro applied to include her wife on her health insurance plan. Federal officials cited DOMA and refused the request. Rather than receive a routine benefit for married spouses, Ms. Coderre had to pay $635 a month to purchase her own health insurance policy.

Vorro estimates the extra cost may ultimately reach $150,000. The sole reason for the extra cost, she said, is DOMA.

“As Rosa Parks might have said, it is time to get up from the back of the bus and assume our seats among our fellow human beings,” Coderre said.

Robin Garber of Staten Island has been married for five years to Kathleen Cumiskey. She said whenever the couple travels from state to state in the US they must bring a box of legal documents – including wills, health-care proxies, and powers of attorney – to be able to prove their legal commitment and responsibility to each other in the event of an emergency.

In contrast, Ms. Garber said, the couple can travel overseas to Spain, Ireland, and South Africa without their documents because in each of those countries their marriage is fully recognized and respected.

Robert Koehl, a professor of classical archaeology at New York’s Hunter College, and his partner, Stylianos Manolakakis, have been together for 15 years. Mr. Manolakakis is a Greek citizen who has been living in the US on a visa. Although the two New York residents could get married under New York law, that marriage would not be recognized by the federal government, including immigration officials.

They have been advised by their lawyer to postpone any marriage plans until Manolakakis’s immigration status can been resolved.

If they were a heterosexual couple, their marriage would speed the immigration process and ensure that they were not separated by national borders. Instead, they say, DOMA stands in the way.

“If DOMA got repealed, we would get married the following day,” Mr. Koehl said.

“I am nearly 60 years old,” he said. “How much longer will I have to wait to enjoy the stability of a marriage with my long-term partner without the fear that at any time we will have to separate?”