General Hayden told the hearing that everything carried out while he ran the military National Security Agency (NSA) was legal and also contended that spy services had to become less of a "political football".
Ruling Republican and opposition Democratic senators raised the controversy over the wiretapping of calls without warrants and new reports that the NSA built up a huge database to log telephone numbers used by tens of millions of Americans.
"There are privacy concerns with everything that we do, of course. We always balance privacy and security, and we do it within the law," General Hayden told the Senate Intelligence Committee.
He insisted that any programs introduced since the September 11, 2001 attacks on New York and Washington were intended to capture Al-Qaeda terrorists and not spy on ordinary Americans.
But General Hayden refused to confirm or deny the existence of the database of calls, first reported last week by USA Today.
‘Confidence in Hayden’
The White House moved to smooth the way for Hayden's nomination this week by agreeing for the first time to brief the full intelligence committees of the Senate and House of Representatives on the eavesdropping on international calls without warrants.
"We've got a lot of confidence in General Hayden," said White House spokesman Tony Snow.
"This is a guy who has been appointed precisely because he's the most qualified intelligence officer in the country. The guy's got a record of trying to take on big reform tasks and carrying them out," he said.
But senators sharply questioned Hayden's credibility for keeping all but a handful of congressional leaders in the dark about the eavesdropping program begun after the September 11 attacks.
"What's to say that if you're confirmed to head the CIA we won't go through exactly this kind of drill with you over there?" said Senator Ron Wyden, a Democrat.
Senator Olympia Snowe, a Republican, said the decision to limit briefings on the secret programs to a so-called "gang of eight" congressional leaders "breeds corrosive mistrust and distrust. In essence, it undermines all of our authority," she said.
General Hayden said he pushed for congressional notification at the outset of the program.
Political football
In his opening remarks, the general called for the CIA to be removed from the political arena following high profile criticism of its failed intelligence before the Iraq war and over the September 11 attacks.
"I believe that the American intelligence business has too much become the football in American political discourse," he said.
"Over the past few years, the intelligence community and the CIA have taken an inordinate number of hits - some of them fair, many of them not. There have been failures but there have also been many great successes."
He also alluded obliquely to charges that intelligence had been manipulated for political ends under President George W. Bush.
"When it comes to 'speaking truth to power', I will lead CIA analysts by example," he said. "I will - as I expect every analyst will - always give our nations leaders the best analystic judgements," he said.
General Hayden said he was uncomfortable with a Pentagon assessment before the Iraq war that asserted connections between Iraqi leader Saddam Hussein and al-Qaeda.
General Hayden indicated he intends to restore the CIA's prestige by focusing on its expertise in espionage, and as the main provider of analysis to the president.