The Vatican has confirmed Cardinal Ratzinger's signature
The Pope is facing allegations he was responsible for delaying Church action against a paedophile priest - the first time he has been accused so directly.
The allegations stem from a letter signed by Benedict XVI in 1985, when he was a senior Vatican official.
Associated Press said it had obtained the letter, signed by Cardinal Joseph Ratzinger, resisting the defrocking of offending US priest Stephen Kiesle.
The Vatican says he was exercising due caution before sacking the priest.
Cardinal Ratzinger - who was at the time the head of the Congregation for the Doctrine of the Faith - said the "good of the universal Church" needed to be considered in any defrocking, AP reported.
By David Willey,
BBC News, Rome
The Vatican claims the letter must be considered in its true context of a lengthy exchange of correspondence between California and Rome about defrocking an American priest who was a known child molester.
The Pope's critics claim that he stalled and left unanswered for years letters concerning alleged cases of sexual abuse by priests.
American bishops are coming under increasing pressure from their flocks to explain why the church in Rome did not take more robust action or took no action at all.
So they are releasing confidential documents which put the future Pope's lack of action in a bad light.
The Vatican insists that the Pope was only exercising due caution before sacking a priest for sexual misconduct.
Vatican officials say the letter was part of a long correspondence and should not be taken out of context.
Vatican spokesman Rev Federico Lombardi said: "The press office doesn't believe it is necessary to respond to every single document taken out of context regarding particular legal situations."
The allegations come as the Vatican says the Pope is willing to meet more victims of clerical abuse, and as the Vatican prepares to publish a guide on the internet about how bishops should deal with accusations of sexual abuse.
The Catholic Church has been hit by a series of child abuse scandals, including in Ireland, the US, Germany and Norway, and has faced criticism for failing to deal adequately with the problem.
AP said the Rev Kiesle was sentenced to three years of probation in 1978 for lewd conduct with two young boys in San Francisco. It said the Oakland diocese had recommended Kiesle's removal in 1981 but that that did not happen until 1987.
Cardinal Ratzinger took over the Congregation for the Doctrine of the Faith, which at the time dealt with some sex abuse cases, in 1981.
ALLEGATIONS FACING POPE
In 1980 as archbishop of Munich and Freising, then-Cardinal Joseph Ratzinger unwittingly approved housing for a priest accused of child abuse. A former deputy later said he made the decision
Cardinal Ratzinger failed to act over complaints during the 1990s about US priest Lawrence Murphy, who is thought to have abused some 200 deaf boys in Wisconsin
Cardinal Ratzinger allowed a case against Arizona priest Michael Teta to languish at the Vatican for more than a decade despite repeated pleas for his removal
Cardinal Ratzinger resisted the defrocking of California priest Stephen Kiesle, a convicted offender, saying "good of the universal Church" needed to be considered
The Pope's supporters say he has been unfairly blamed for cases handled by junior staff, and that he has been proactive in addressing child abuse.
AP says the 1985 correspondence, written in Latin, shows Cardinal Ratzinger saying that Kiesle's removal would need careful review.
Cardinal Ratzinger urged "as much paternal care as possible" for Kiesle.
Kiesle was sentenced to six years in prison in 2004 after admitting molesting a young girl in 1995.
Kiesle is now 63 and is on the registered sex offenders list in California.
On Friday, the Vatican urged Catholic dioceses around the world to co-operate with police investigating sex abuse allegations against priests.
Father Lombardi acknowledged that the Church had lost public trust and said Church law could no longer be placed above civil laws if that trust were to be recovered.
He also said Pope Benedict was prepared to meet more victims of abuse to offer them moral support.
BBC religious affairs correspondent Robert Pigott says this is an abrupt change of tone by the Vatican.
He says officials had previously accused critics of trying to smear the Pope personally and only last weekend said he should ignore petty gossip directed at him.
Meanwhile Italian media have reported that the Vatican is to issue guidelines on its website on Monday on fighting paedophilia.
The Vatican has ruled out any possibility of a papal resignation over the scandals.