WASHINGTON — Now it can be told: A prominent gay rights advocate who called himself J. D. Smith is in fact 1st Lt. Josh Seefried, a 25-year-old active-duty Air Force officer. At 12:01 a.m. Tuesday, he dropped the pseudonym, freed from keeping his sexual orientation secret like an estimated tens of thousands of others in the United States military.

“I always had the feeling that I was lying to them and that I couldn’t be part of the military family,” said Lieutenant Seefried, who helped found an undercover group of 4,000 gay, lesbian, bisexual and transgender active-duty service members. “I feel like I can get to know my people again. When I go to a Christmas party, I can actually bring the person I’m in a relationship with. And that’s a huge relief.”

The 18-year-old “don’t ask, don’t tell” policy officially ended at midnight and with it the discharges that removed more than 13,000 men and women from the military under the old ban on openly gay troops. To mark the historic change, gay rights groups are planning celebrations across the country while Defense Secretary Leon E. Panetta and Adm. Mike Mullen, the chairman of the Joint Chiefs of Staff, will usher in the new era at a Pentagon news conference.

The other side will be heard, too: Elaine Donnelly, a longtime opponent of allowing gay men and lesbians to serve openly in the armed forces, has already said that “as of Tuesday the commander in chief will own the San Francisco military he has created.” Two top Republicans on the House Armed Services Committee — the chairman, Representative Howard P. McKeon of California, and Representative Joe Wilson of South Carolina — have asked the Pentagon to delay the new policy, saying commanders in the field are not ready. But the Pentagon has moved on.