VATICAN CITY -- A day ahead of his formal installation, Pope Francis met privately on Monday with Cristina Fernández de Kirchner, the president of his native Argentina, with whom he had clashed over social issues such as Argentina's legalizing gay marriage.
The two met for 15 minutes of private conversation before a lunch together, the Vatican said. It did not issue a statement, but in a news conference later in Rome, Mrs. Kirchner said she had found the pope, the former Cardinal Jorge Mario Bergoglio of Buenos Aires, "calm, confident and at peace, tranquil."
"I could also say that he is occupied and concerned about the immense task not only to govern Vatican City State, but to change things that he knows need to change," she added.
She also said she had asked Francis to intervene in the dispute over the Falkland Islands, which Argentina claims as its own but whose residents just voted to remain part of Britain.
For many years, the relationship between Francis and Mrs. Kirchner has been depicted as mutually hostile, as it was between him and her husband and predecessor, Néstor Kirchner, who died in 2010.
Underlying the strains have been accusations -- dismissed by the Vatican -- of complicity between the church in Argentina and the military dictatorship of the 1970s and early 1980s in the so-called Dirty War, when as many as 30,000 people are thought to have been killed or "disappeared."
As the leader of Argentina's Jesuits for part of that time, Cardinal Bergoglio has repeatedly disputed claims that he allowed the kidnapping of two priests in his order in 1976, accusations the Vatican is calling a defamation campaign.
But the tensions sharpened more recently over doctrinal issues that reflect Francis' deep conservatism on the social issues that often divide Catholics.
Francis has been -- and remains -- a staunch supporter of the Vatican's positions on abortion, the ordination of women, gay marriage, adoption by gay couples and other major issues.
In 2010, he described a government-supported law in Argentina to legalize marriage and adoption by same-sex couples as "a war against God" and "a maneuver by the devil."
At the time, Mrs. Kirchner called his position "medieval."
The Vatican said representatives of 132 countries and international organizations were expected to attend the installation Mass on Tuesday. One who is raising eyebrows is Robert G. Mugabe, the autocratic president of Zimbabwe. He is the subject of a travel ban by European countries because of Zimbabwe's human rights record, but exemptions allow him to travel to Vatican City, which is encircled by Italian territory, and to United Nations gatherings.
The Vatican spokesman, the Rev. Federico Lombardi, said the Vatican does not issue invitations. "Those who wish to come, can," he said. "No one is refused. No one is invited. We welcome those who want to come."
Vice President Joseph R. Biden Jr., who is Catholic, will represent the United States at the Mass. The delegation also includes Gov. Susana Martinez of New Mexico; Representative Nancy Pelosi of California, the Democratic leader of the House; and John J. DeGioia, the president of Georgetown University, a Jesuit institution.
Francis is the first Jesuit pope and the first pope from Latin America.
At the installation Mass, Francis is expected to receive the fisherman's ring, which recalls how St. Peter fished for food and later for souls, and the pallium, a white woolen vestment that symbolizes the role of the pope as a good shepherd. The ring was made from gold-plated silver by an Italian jeweler, Enrico Manfrini.
Rachel Donadio reported from Vatican City, and Alan Cowell from London. Elisabetta Povoledo and Gaia Pianigiani contributed reporting from Rome.
This article originally appeared in The New York Times.