Hayden said the plutonium reactor was within weeks or months of completion when it was destroyed in an air strike last September 6, and within a year of entering operation it could have produced enough material for at least one weapon.
"In the course of a year after they got full up, they would have produced enough plutonium for one or two weapons," Hayden told reporters after a speech.
The reactor was of a "similar size and technology" to North Korea's Yongbyon reactor, Hayden said, disputing speculation it was smaller than the Korean facility.
"We would estimate that the production rate there would be about the same as Yongbyon, which is about enough plutonium for one or two weapons per year," he said.
Hayden's comments were the first statement on the suspected reactor's capacity, and his first public remarks since the United States released photos of what it said was a secret nuclear reactor built with North Korean aid.
A diplomat close to the UN nuclear watchdog and outside analysts have said the US disclosure did not amount to proof of an illicit arms program because there was no sign of a reprocessing plant needed to convert spent fuel from the plant into bomb-grade plutonium.
The United Nations' International Atomic Energy Agency has also criticized the United States for waiting until this month to share its intelligence. The delay complicates the IAEA's effort to confirm whether the facility was a plutonium reactor.
Hayden said the United States lacked the liberty earlier to pass on the intelligence, which he said was acquired in a "team effort." ABC News reported in October that Israel had obtained pictures of the Syrian complex from an apparent mole and showed them to the CIA.
"We did not have complete control of the totality of the information," Hayden said. US officials have declined to identify sources of the intelligence.
Asked whether Washington had eventually gotten approval to pass on the intelligence, Hayden said, "One would never share the intelligence without consultation with that nation, as a general principle."
A senior Bush administration official said at a briefing last week the intelligence was disclosed this month in part to pressure North Korea in disarmament talks to fully acknowledge its nuclear and proliferation activities, and to widen the circle of U.S. lawmakers briefed on the issue.
Congressional support is key to President George W. Bush's goal of making progress toward ending North Korea's nuclear ambitions.
Senior intelligence officials said at the briefing they told Bush the Syrian facility was a plutonium reactor built with North Korean cooperation and intended to fuel a nuclear weapons program.
They acknowledged their confidence level was relatively low over its purpose as a weapons facility, due to limited evidence.
The officials said there was no reprocessing facility in the area of the destroyed reactor, but declined to further discuss their views of any Syrian reprocessing capability.