After being denied entry at Kennedy Airport without explanation nearly four years ago, the South African Muslim scholar Adam Mahomed Habib was in Atlanta this weekend to give a talk at a sociology conference. His subject? Making democratic governments more accountable to the people.
Mr. Habib, a deputy vice chancellor at the University of Johannesburg, was one of a number of foreign scholars barred in recent years from entering the United States by the Bush administration.
The American Civil Liberties Union took up his case along with that of Tariq Ramadan, a controversial scholar of the Islamic world, arguing that the administration was keeping out critics and violating the First Amendment rights of American scholars who wanted to hear them.
Mr. Habib, who attended graduate school at the City University of New York and frequently visited the United States, was never told the specific reason he was barred from entering in October 2006. But he and his supporters suspect it was because of his vocal criticism of the war in Iraq and United States foreign policy in general.
After two court cases, a deal was struck this January permitting Mr. Habib and Mr. Ramadan to enter the country.
In Atlanta for the annual conference of the American Sociological Association, Mr. Habib said the agreement with the State Department still did not reveal the reason for his exclusion. "It said, 'We won't tell you why, but we won't apply the rationale anymore,' " Mr. Habib said on Saturday after participating in a panel on rebuilding societies after natural and social disasters.
Mr. Habib said he had addressed antiwar rallies in South Africa and participated in peaceful marches to the American and British Embassies, but that he had never advocated any kind of violence.
"I got lucky that there were institutions that took up my case," Mr. Habib said, referring to the sociological association, which for the past few years has been inviting him to appear at its conference, as well as the A.C.L.U., the American Association of University Professors and other organizations. His experience shows the importance of "academic solidarity," he said.
In his speech this weekend, there were no clues as to why the Department of Homeland Security might have worried about his appearing at a previous conference of sociologists. Speaking to a sparsely filled ballroom of about 50 people, Mr. Habib talked about empowering poor people in his home country by strengthening opposition parties and reforming the electoral system to have more direct representation. Despite the extraordinary success of ending apartheid without civil war, South Africa's poor "could be worse off today than 15 years," he said.
Mr. Habib received a 10-year visa and is required to notify the Department of Homeland Security before visiting the United States.
The hardest part of the ban, which also applied to his family, was telling his 10-year-old son in 2006 that he could not take part in a student exchange program in Washington, D.C., for which he had been selected: "How do I explain it to him?"