Mr. Gansler's move is expected to draw legal and legislative challenges, but for Terrance Heath of Montgomery County, Md., it was the turning point that persuaded him to get married.
"We realized that we can finally get many of the benefits and protections that other couples take for granted," said Mr. Heath, 41, a blogger who lives with his partner, Rick Imirowicz, 43, and their two adopted sons.
"Before that attorney general decision we could have the legal documents, like wills and medical power of attorney," Mr. Heath said. "But there was no guarantee that those documents would be recognized."
He said that he and Mr. Imirowicz had worried about what might happen to any inheritance meant for their sons, Parker, 7, and Dylan, 2. "Marriage gives us peace of mind," Mr. Heath said. "It gives my family security that we deserve."
At the city's Marriage Bureau inside the Moultrie Courthouse, just blocks from the Capitol, the mood was giddy as couples hugged and talked about a day they never thought would arrive.
"I became a naturalized U.S. citizen in the mid-'90s," said Cuc Vu, a native of Vietnam who was third in line with her partner of 20 years, Gwen Migita. "But this is really the first time that I feel like I have the full rights and benefits of citizenship."
Court officials explained that the Marriage Bureau had changed its license applications: They ask for the name of each spouse rather than the bride and groom. Officials who perform the weddings read, "I now pronounce you legally married."
On a typical day the office processes 10 licenses, court officials said. By late Wednesday afternoon, more than 140 couples had filed to be married, the mayor's office said.
Because of a mandatory waiting period, couples will not be able to marry in the city until Tuesday.
City officials say the measure will also provide a financial boost to the local economy. A study by the Williams Institute at the University of California, Los Angeles, predicted that more than 14,000 same-sex marriages would occur in the city over the next three years, which would bring in $5 million in new tax revenue and create 700 jobs.