John Brennan said Thursday that the attack could have killed other people as well as bin Laden, and that the chances for success were minimal.
He also told the Senate Intelligence Committee the information supporting the attack was "not well grounded."
He said he was among numerous intelligence officials who urged against such an attack. Their advice was followed.
Brennan was the CIA station chief in Saudi Arabia at the time of the embassy bombings.
Three years later, on Sept. 11, 2001, bin Laden launched the deadliest terrorist attacks in U.S. history.