WASHINGTON — Breaking ranks, a career FBI agent told members of Congress yesterday that the bureau lacked the experience and sophistication to deal with Middle Eastern terrorists and prevent another catastrophic attack.

Agent Bassem Youssef said counterterrorism agents and managers at FBI headquarters often lack basic knowledge about Middle Eastern culture, language, and terrorists’ ideology. Compounding matters, he said, is the fact that the FBI has continued to name supervisors to anti-terror positions who have little or no experience outside traditional law enforcement.

The result, he said, is that agents are wasting resources chasing leads that more sophisticated observers would quickly dispense with. The time and energy expended on marginal cases has diverted resources from investigating more substantial threats, he said.

“The FBI counter-terrorism division is ill-equipped to handle the terrorist threat we are facing,” Mr. Youssef told a House Judiciary Committee subcommittee considering legal protections for government whistle-blowers working at national security agencies such as the FBI. “Regardless of what happens to me when I walk into the Hoover (FBI headquarters) building tomorrow, that is what I hope to convey to you,” Mr. Youssef, who was one of several who testified at the hearing, said.