ON SUNDAY, gay and lesbian couples in New York will finally be able to marry in their home state. But the legal and moral victory for these couples and those in a handful of jurisdictions that recognize same-sex marriage will not be complete until the federal government eliminates its discriminatory policies.

Congress inched closer to that goal this week by holding the first hearing ever to discuss repeal of the Defense of Marriage Act. DOMA, which was signed into law by President Bill Clinton in 1996, defines marriage as the union of one man and one woman. The law is as simple as it is perverse, with the intention of excluding same-sex married partners and denying them some 1,000 federal benefits available to their heterosexual counterparts.

Ron Wallen, 77, told the Senate Judiciary Committee how he was denied Social Security survivor benefits after his partner of more than 50 years died this year. He and his partner were married in California in the few months in 2008 when same-sex marriage was legal there.

Andrew Sorbo, 64, a Connecticut resident who lost his partner of nearly 30 years, noted how he was denied pension benefits from the Veterans Administration. Mr. Sorbo, who married his partner in 2009, told of other financial hardships he was forced to bear because of DOMA. “I quickly discovered that my legal Connecticut marriage license was paper-thin in the eyes of the federal government,” he said.

The hearing convened by Chairman Patrick J. Leahy (D-Vt.) took up the Respect for Marriage Act, which was introduced by Sen. Dianne Feinstein (D-Calif.) and Rep. Jerrold Nadler (D-N.Y.) to repeal DOMA. In testimony, Rep. John Lewis (D-Ga.), the legendary civil rights leader, compared the discrimination against same-sex unions to prohibitions in the 20th century against interracial marriages: “We look back at that time now with disbelief, and one day we will look back on this period with that same sense of disbelief.” Mr. Lewis’s colleagues in the House should advance the bill.

President Obama gave the bill a welcome boost on the eve of the hearing. This is not the first time he has called for DOMA’s repeal, but it was important that he did so now that a bill is under consideration. When, as Mr. Lewis said, people look back decades from now, it will be reassuring to know that the White House was on the right side of this defining civil rights issue.