WASHINGTON — A gunman, spouting opposition to social conservatism, walked into the Washington headquarters of a conservative lobbying group Wednesday and shot a security guard before the wounded guard and others wrestled him to the floor and subdued him until police arrived, authorities said.

They identified the suspect as Floyd Lee Corkins II, 28, of Herndon, Va., who has a master's degree from George Mason University's College of Education and Human Development, in northern Virginia. Corkins was in FBI custody Wednesday night; authorities had not filed charges against him.

The guard, identified by the lobbying group, the Family Research Council, as Leo Johnson, was shot in the arm before or during the incident in the lobby, Washington Police Chief Cathy Lanier said. She credited Johnson with preventing a tragedy by stopping the man, who was carrying a 9 mm handgun, from reaching the upstairs offices in the group's six-story building near downtown Washington.

"The security guard here is a hero, as far as I'm concerned," Lanier said. "He did his job; the person never made it past the front."

Johnson was hospitalized in stable condition, authorities said. No one else was injured.

The FBI said it was evaluating evidence to determine whether to charge Corkins with a federal crime, such as attempting a terrorist act. Authorities said the decision will hinge on what the FBI concludes was the assailant's motive for entering the building with a loaded Sig Sauer semiautomatic.

Officials said Corkins' gun was bought legally within the past several weeks.

TV news footage showed the suspect, a large man with a shaved head, being led to a car in hand restraints.

Officials, who were interviewing Corkins, also went to his Herndon home and interviewed his family and neighbors.

The Family Research Council deals in issues of faith, family and freedom, its website says. The organization opposes abortion and euthanasia, among other practices, and says it considers homosexuality to be a sin.

The group's headquarters is in the city's bustling Chinatown neighborhood, near the Verizon Center, the Smithsonian National Portrait Gallery and several museums, restaurants and shops.

Social-issues groups on the left and right and both presidential candidates weighed in on the shooting. Gary Bauer, a former president of the Family Research Council and now head of American Values, cited "a disturbing level of intolerance and hate aimed at those who share traditional values."

"Men and women of faith must not be intimidated into silence," Bauer said.

Speaking for several lesbian, gay, bisexual and transgender organizations, the Gay & Lesbian Alliance Against Discrimination said: "We utterly reject and condemn such violence" and "wish for a swift and complete recovery for the victim of this terrible incident."

The shooting drew statements both from Republican presidential candidate Mitt Romney and President Obama.

"There is no place for such violence in our society," Romney said, adding that he would pray for council employees whose sense of security has been shattered.

Administration spokesman Jay Carney said Obama expressed concern for the security guard and said: "This type of violence has no place in our society."

Two law-enforcement officials, speaking on condition of anonymity, said the gunman entered the lobby carrying a satchel, with a bag from a Chick-fil-A restaurant inside. The Atlanta-based fast-food chain has been embroiled in controversy in recent weeks after its president spoke out against same-sex marriage. The Family Research Council also opposes such unions.

"Today's attack is the clearest sign we've seen that labeling pro-marriage groups as 'hateful' must end," said Brian Brown, president of the National Organization for Marriage.

Corkins had been volunteering at a Washington community center for gay, lesbian, bisexual and transgender people, according to officials there. Michael Sessa, president of the D.C. Center for the LGBT Community, said the FBI has spoken with staff members about Corkins, who had been volunteering for about six months.

Material from The Associated Press is included in this report.