Still, some members of Congress and security experts say the arrest of Mr. Jayab has forced them to question the screening process. Federal court documents show that at least 14 people who came to the United States as refugees have been arrested on terrorism charges in the last two years, including Mr. Jayab.

“I thought that it was very secure until I saw the arrest in California and Texas,” said John J. Farmer Jr., former senior counsel to the federal commission that investigated the Sept. 11 terrorist attacks, who is now a professor at Rutgers. “Now, I have my concerns.”

The federal authorities charged that Mr. Jayab conspired with Omar Faraj Saeed Al Hardan, 24, an Iraqi-born refugee living in Houston, to get weapons training and eventually sneak into Syria to fight alongside terrorist groups.

Benjamin Galloway, a federal public defender in Sacramento and Mr. Jayab’s lawyer, said his client had done nothing wrong. “There is no threat that this man poses and no indication that he’s engaged in any activity since his return two years ago,” he said.

Many of the Paris attackers were European citizens and could have entered the United States under the visa waiver program. Tashfeen Malik, one of the attackers in San Bernardino, was granted entry to the United States on a K-1 visa, which can be given to the fiancé or fiancée of an American citizen. And a number of refugees from Bosnia, Iraq and Somalia have been arrested and charged with supporting terrorists.

Homeland Security officials say the refugee screening process has a much lower security risk.

Refugees recommended for resettlement in the United States first undergo screening abroad, by the Office of the United Nations High Commissioner for Refugees. In addition to intensive interviews, the agency collects biometric data such as iris scans and photographs.

In the United States, refugees face another round of intense screenings and interviews by caseworkers at the United States Citizenship and Immigration Services in Washington. Their names are run through law enforcement and intelligence databases at the National Counterterrorism Center, the F.B.I., the Defense Department, the State Department and United States Customs and Border Protection, among other agencies.