"To the contrary ... we were told explicitly that waterboarding was not being used," she told reporters, referring to a formal CIA briefing she received in the fall of 2002.
Pelosi said she subsequently learned that other lawmakers were told several months later by the CIA about the use of waterboarding.
"I wasn't briefed, I was informed that somebody else had been briefed about it," she said.
Pelosi said under secrecy laws she was powerless to talk about or do anything to stop it, reports CBS News correspondent Bob Fuss reports.
The House's top Democrat made her comments at a news conference where she was peppered with questions about her knowledge of a technique she and others have called torture. Republicans have insisted in recent weeks that Pelosi and other Democrats knew waterboarding was in use, but made no attempt to protest.
In a written response issued moments after Pelosi spoke, an official at the CIA neither disputed nor accepted the California Democrat's statements.
Instead, George Little, head of the CIA office of public affairs, said it would be up to Congress to determine whether notes made by agency personnel at the time they briefed lawmakers were accurate. He said the notes could be made available at the CIA "for staff review."
Pelosi says she was only briefed once about harsh interrogation methods and was not told waterboarding was being used against top al Qaeda detainees. But the the CIA pointed to recently released documents that raise questions about Pelosi's account, reports CBS News correspondent Bob Orr.
A declassified Justice Department memo shows that Abu Zabaydah was waterboarded "at least 83 times in August 2002"
Pelosi was briefed after that, on Sept. 4, 2002, Orr reports.
According to CIA records she was told about "EITs (enhanced interrogation techniques) on Abu Zubaydah … and a description of particular EITs that had been employed."
Republicans say Pelosi and other democrats were fully in the loop. Between 2002 and 2007, CIA records show, intelligence committee members from both parties received at least 28 classified briefings on harsh interrogations.
Pelosi renewed her call for a so-called truth commission to investigate the events in the Bush administration that led to the use of waterboarding and other harsh interrogation techniques. While President Barack Obama has banned waterboarding, calling it torture, he has been notably cool toward an independent inquiry that might distract attention from his domestic agenda.
Senate Majority Leader Harry Reid, D-Nev., also has expressed opposition, as have congressional Republicans.
Pelosi was particularly harsh in describing the CIA.
"They mislead us all the time," she said. And when a reporter asked whether the agency lied, she did not disagree.
She also suggested that the current Republican criticism marked an attempt to divert attention from the Bush administration's actions.
"They misrepresented every step of the way, and they don't want that focus on them, so they try to turn the attention on us," she said.
Pelosi contended that Democrats did what they could to stop the use of waterboarding. The senior Democrat on the Intelligence Committee, who received the 2003 briefing on the practice, sent the CIA a formal letter of protest, she said.
But Pelosi defended her own lack of action on the issue, saying her focus at the time was on wresting congressional control from Republicans so her party could change course.
"No letter could change the policy. It was clear we had to change the leadership in Congress and in the White House. That was my job - the Congress part," Pelosi said.