Pope Benedict XVI was hit by fresh allegations yesterday that he failed to crack down on sexually abusive Catholic priests before becoming pontiff.

A letter written in 1985, when the then Cardinal Joseph Ratzinger was the head of the Vatican's doctrinal unit, resists a request for the defrocking of an American priest with a record of molesting children, for the "good of the universal Church".

The letter, published by Associated Press, also notes the "detriment that granting the dispensation can provoke within the community of Christ's faithful, particularly considering the young age". The priest, Father Stephen Kiesle, was 38 at the time.

Father Federico Lombardi, a Vatican spokesman, confirmed the cardinal's signature on the letter, but added: "The press office doesn't believe it is necessary to respond to every single document taken out of context regarding particular legal situations."

But the letter does switch the spotlight back to Benedict as a wave of sex abuse scandals involving priests, as well as alleged cover-ups by their bishops, sweeps Europe and the US. The Vatican has previously denied reports suggesting Benedict failed to tackle cases of abuse in Munich and Wisconsin before he became pope. Kiesle was sentenced in 1978 to three years' probation after pleading no contest to charges of lewd conduct for tying up and molesting two young boys in a San Francisco rectory.

In 1981 he asked to leave the priesthood, a request backed by his diocese, which forwarded the papers to Rome. In 1982, Oakland bishop John Cummins urged Ratzinger, as head of the Vatican's congregation for the doctrine of the faith, to grant the request.

But the case was still pending in 1985 when Ratzinger wrote to Cummins that although the argument for defrocking Kiesle was of "grave significance", it was necessary "to submit incidents of this sort to very careful consideration, which necessitates a longer period of time".

Another priest, George Mockel, wrote to Cummins: "My own reading of this letter is that basically they are going to sit on it until Steve gets quite a bit older," reported AP.

Kiesle was finally removed in 1987, but in the meantime had carried out volunteer work with children through the church. He was arrested and charged in 2002 with 13 counts of child molestation from the 1970s, but all but two were thrown out after the US supreme court struck down as unconstitutional a California law extending the statute of limitations. He was later sentenced to six years in jail in 2004 for molesting a young girl in 1995. He is now 63 and a registered sex offender.

"The then cardinal Ratzinger did not cover up the case, but as is clearly shown by the letter, he indicated the need to study the case with greater attention," said the Vatican's assistant spokesman Ciro Benedettini.

In an editorial published yesterday on the website of Vatican radio, Lombardi said the pope had become the victim of "unfounded insinuations and criticisms", and recalled the offer made by Benedict to meet abuse victims in a letter to Irish Catholics last month.

The experience the church has gained in battling abuse in its ranks "could be useful to other institutions and society as a whole," he added. "It seems that the media has not considered this aspect sufficiently."