And he would do it again if he had the chance, "because offenses against my people and my fellow partisans are as many ways as bad," he said.
He planned his killings as a suicide attack, he said.
"I didn't expect to survive that day," he said.
Breivik testified in closed court a day after declaring that he had carried out the massacre but was not guilty because the killings had been necessary.
"I acknowledge the acts but do not plead guilty," he told the court Monday.
A court translator initially said Breivik was claiming self-defense as the justification, but court officials corrected that Tuesday, saying the correct legal term was "necessity."
His lawyer, Geir Lippestad, said Monday that he would try to show that his client was sane when he set off a bomb that killed eight people in central Oslo and then systematically gunned down 69 people at a youth camp on nearby Utoya Island.
Breivik's trial on charges of voluntary homicide and committing acts of terror is expected to last up to 10 weeks.
On Tuesday, he rejected what he said would be prosecution efforts to portray him as a "pathetic and mean loser" and an "antisocial psychopath."
He said he represented a "European resistance movement" and "Europeans who don't want our ethnic rights to be taken away."
Under examination by prosecutors, he claimed to be linked to two other individuals in Norway who are associated with the so-called Knights Templar ultranationalist movement.
He said "militant nationalists" had drawn tactical inspiration from Osama bin Laden's terror network.
"We've taken a bit from al Qaeda and militant islamists, including the glorification of martyrdom" and organization into one-man cells, he said.
He denied that what he called the "militant nationalist" movement was evil.
"We don't act to be evil. We're trying to save our nations, our ethnic group and our culture," he said.
One of the judges was disqualified Tuesday before the hearing began for saying online that the death penalty was the right punishment for Breivik.
Defense and prosecutor attorneys both asked that Thomas Indrebo be disqualified for leaving a comment on a news website that "only the death penalty" would be the right thing in the case. Norway does not have the death penalty.
Breivik smirked as presiding Judge Wenche Elizabeth Arntzen laid out the objection.
Arntzen ruled that his testimony would not be broadcast, rejecting his claim that airing it was a human right.
Most of the relatives of the victims did not want Breivik's remarks broadcast.
"It's going to be 10 weeks of hell ... to hear this man, to hear his explanation of why he did it and how he did it," said Trond Henry Blattmann, whose son was killed on Utoya Island.
Breivik says his rampage was meant to save Norway from being taken over by multicultural forces and to prevent ethnic cleansing of Norwegians, Lippestad said.
In a 1,500-page manifesto attributed to him, Breivik railed against Muslim immigration and European liberalism, including the Labour Party, which he said was allowing the "Islamification of Europe."
Prosecutors on Monday played a recording of a terrified girl phoning for help during the shooting rampage, a recording punctuated by constant firing in the background. They also showed security camera video of the central Oslo bomb blast that killed eight people, images that participants in the trial watched with ashen faces.
Breivik sat in court without restraints, behind a bulletproof glass barrier set up to protect him during the proceedings.
Experts have given different opinions about Breivik's sanity, which will be a factor in determining what punishment he receives if convicted. Sentencing options could include imprisonment or confining him to a mental facility.
Prosecutors on Monday outlined Breivik's life before the killings, showing a photo of the messy room where he lived at his mother's house, listing his six failed businesses and referring to his many hours playing the online game "World of Warcraft." Prosecutors said he had "no job, no salary, no money from the government" and was "living off his savings."
The defendant smiled briefly when his "Warcraft" character was shown, one of the few times he showed emotion Monday.
He also appeared to be overcome with emotion, fighting back tears, when part of his video manifesto "Knights Templar 2083" was played in court.
On Tuesday, he said he wept as he watched the film because he was thinking about his country and ethnic group dying.
Lawyers for the victims had said Monday that "No one thought he was crying for the victims."
In November, prosecutors said psychiatrists had determined that Breivik was paranoid and schizophrenic at the time of the attacks and during 13 interviews experts conducted with him afterward. However, the court sought a second opinion because of the importance of the question of sanity to Breivik's trial.
In a report released this month, two court-appointed psychiatric experts said Breivik was sane at the time of the killings.