Henry Rousso, a French historian and one of the most pre-eminent scholars on the Holocaust, said he was detained for more than 10 hours by federal border agents in Houston and told he would not be allowed to enter the United States before lawyers intervened to stop his deportation.

Mr. Rousso said in a telephone interview on Sunday that he arrived at the George Bush Intercontinental Airport around 2 p.m. Wednesday on a flight from France when immigration authorities began to question his visa and his reason for being in the United States.

Mr. Rousso, an expert on France after the First World War, was scheduled to give a keynote address on Friday afternoon at a conference organized by the Hagler Institute for Advanced Study at Texas A&M University in College Station.

“It would be in no means difficult to look up who he is,” said Jason Mills, an immigration lawyer who helped secure Mr. Rousso’s eventual release. “His reasons for being here were nothing but beneficial to the United States. He is a man of experience and age,” Mr. Mills said. “There is plenty of history there on him. I don’t understand why he would have been in for the several hours that he was. It is a little alarming.”