He promised that his government will investigate how Nazis were allowed to enter Argentina after World War II and punish anyone who committed crimes and may still be at large.
Referring to how Nazis were smuggled in or received visas, de la Rua said, "I apologize that this was allowed to happen This we regret with a deep feeling of pain."
He said it was important for present and future generations to publicize these events "to avoid any repetition, to prevent other forms of xenophobia and racism from taking root."
De la Rua said he had apologized twice before for the sanctuary his country offered Nazis, "but it is important to repeat it and express solidarity with the victims of the Holocaust."
The Washington representative of the World Jewish Congress, Douglas Bloomfield, listened to de la Rua's statement and called it "commendable and very important."
De la Rua said the apology was appropriate because "Nazi war criminals took advantage of an opportunity to find shelter in Argentina" as some consular officials were making it difficult for Jews to get visas.
"This is my regret," de la Rua said a news conference in a hotel near the White House. "A commission has been created to open all Nazi files and find the truth, and its work will continue."
De la Rua met later with President Clinton and planned also to carry his message of forgiveness to a ceremony at the Holocaust Museum. In addition, he will meet with Jewish leaders.
The Argentine leader also said investigators again will probe the 1992 bombing of the Israeli Embassy in Buenos Aires and an attack two years later on a Jewish community center in the Argentine capital.
The embassy bombing killed 29 people, and 86 died in the attack on the center.
"We plan to find out the truth and want justice to be done," de la Rua said.
In Buenos Aires recently, de la Rua said, he hosted a luncheon at his residence in honor of Holocaust survivors.
At a speech last month to mark the 57th anniversary of the April 19-May 16, 1943, Warsaw Uprising by Jews, de la Rua said Argentina had to come to grips with its past, which included harboring wanted Nazi war criminals for decades.
In 1960, Israeli agents abducted Adolf Eichmann, a chief architect of the Holocaust, from his hide-out in Buenos Aires.
And in 1998, Argentine authorities arrested Dinko Sakic, one-time commander at Croatia's Jasenovac concentration camp, who had been living peacefully in Argentina. He was extradited to Croatia, where last year he was sentenced to 20 years in prison for war crimes.
Argentine researchers reported in November 1998 that they had found proof that former Argentine Presient Juan Peron encouraged fleeing Nazi war criminals to seek asylum in his country after World War II. Peron was president between 1945 and 1955.
In addition, Israeli-based groups say the number of Jews purged during the anti-left campaign of the 1976-83 military dictatorship was disproportionately high.
Estimates of the number of Jews who vanished during that period range as high as 2,000, and Israel has asked the de la Rua government to investigate. Argentina is home to about 300,000 Jews, the second largest Jewish community in the Americas.
De la Rua's statement is one of several recent gestures by countries and companies to make amends for their role in the Holocaust and its aftermath.
Dutch banks and the Amsterdam stock exchange recently proposed paying more than $132 million to settle claims they helped the Nazis steal bank accounts and stocks from Jews.
By HARRY DUNPHY