The US administration has briefed members of in Congress on its controversial wiretapping programme.
Mr Bush hopes to ease Gen Hayden's nomination hearings
Officials acquainted full committees from both houses with the domestic programme, which previously only eight legislators had been briefed on.
US media revealed last year that the National Security Agency (NSA) tapped overseas calls by terror suspects.
Further claims followed last week that the agency was collecting phone records of tens of millions of Americans.
President George W Bush has insisted that all such activities are lawful.
But many legal experts say the government needs explicit permission from a special court - which it did not obtain.
The administration began briefing intelligence committees in the House of Representatives and Senate on Wednesday.
The closed-door sessions came a day before confirmation hearings for the nominee for CIA director, Gen Michael Hayden - a former NSA head who oversaw the surveillance programme.
Members of the Senate Select Intelligence Committee said the NSA provided a lot of information, but unanswered questions remained.
"It certainly is going to give new meaning to the concept known as a cram course," Oregon Democratic Senator Ron Wyden told Reuters news agency.
"This is the beginning of something that should have begun years ago."
Correspondents say that by allowing the briefings the administration may be trying to ease what could otherwise be a rocky ride for Gen Hayden.
Senate Intelligence Committee Chairman Pat Roberts said the surveillance issue was "central" to Gen Hayden's hearings.
"It became apparent that in order to have a fully informed confirmation hearing, all members of my committee needed to know the full width and breadth of the president's programme," he said in a written statement.