By Philip Pullella
VATICAN CITY (Reuters) - Pope Benedict marks two milestones this week and while his health appears stable, signs of frailty have again prompted speculation over whether he will be the first pontiff in seven centuries to resign.
Benedict, one of the oldest popes in history, turns 85 on Monday, and on Thursday he marks the seventh anniversary of his election as successor to the immensely popular John Paul II.
Speaking to pilgrims and tourists in St Peter's Square on Sunday, he noted Thursday's anniversary and asked for prayers "so that the Lord may give me the strength to carry out the mission he has entrusted to me".
Benedict is already older than John Paul was when he died in 2005 and is now the oldest reigning pope since Leo XIII, who died aged 93 in 1903 after reigning for 25 years.
"His health at 85 is better than John Paul's was at 75," said one high-ranking Vatican official who reports to the pope regularly. "He is a very methodical man. He looks after himself and feels that he still has much to do," the official said.
The Vatican has announced that he will visit Lebanon in September and he may go to Brazil in 2013.
"I'm old but I can still carry out my duties," the pope told Fidel Castro during his trip to Cuba last month.
Still, Benedict is increasingly showing signs of frailty and fatigue, signs that are being watched carefully for their possible effect on the future of the 1.2 billion member Roman Catholic Church.
When he left for Mexico and Cuba, he used a cane at the airport for the first time in public, though sources say he has been using it in private for some time.
Last year, to conserve his strength, he began using a mobile platform instead of walking up the aisle of St Peter's Basilica.
The Vatican says it is to spare him fatigue and there is no concern about his overall health. His brother has said Benedict suffered two mild strokes before his election in 2005 and he reportedly suffers from high blood pressure and arthritis.
WOULD CONSIDER RESIGNING
Where Benedict differs from his predecessors is that he is the only pope in living memory to discuss publicly the possibility of resignation, though others have done so privately.
In a book in 2010, Benedict said he would not hesitate to become the first pontiff to resign willingly in more than 700 years if he felt no longer able, "physically, psychologically and spiritually" to run the Catholic Church.
"Those of us who are over 75 are not allowed to run even a small diocese and cardinals over 80 are not allowed to elect a pope. I can understand why one day the pope might say 'even I can't do my job any more,'" said retired Archbishop Luigi Bettazzi of the north Italian city of Ivrea.
"I wish him a long life and lasting lucidity but I think that if the moment arrives when he sees that things are changing, I think he has the courage to resign," Bettazzi told Italian television on Saturday.
The last pope to resign willingly was Celestine V in 1294 after reigning for only five months. Gregory XII reluctantly abdicated in 1415 to end a dispute with a rival claimant to the papacy.
Every papal birthday or anniversary sparks talk of succession but there is no clear front runner to succeed Benedict, who has now appointed more than half the cardinals who will choose a new pope from among their ranks. Most are Europeans.
HERO TO CONSERVATIVES
Since his election on April 19, 2005, succeeding one of history's most popular pontiffs, Benedict has been hailed as a hero by conservative Catholics and viewed with suspicion by liberals.
Elected when he was 78 - 20 years older than John Paul was when he was elected - he has ruled over a slower-paced, more cerebral and less impulsive Vatican.
While conservatives have cheered him for trying to reaffirm traditional Catholic identity, his critics accuse him of turning back the clock on reforms by nearly half a century and hurting dialogue with Muslims, Jews and other Christians.
He also has made a series of missteps that angered Jews and Muslims and lowered his popularity among Catholics themselves.
Before he was elected Pope, the former Cardinal Joseph Ratzinger was known by such critical epithets as "God's rottweiler" because of his stern stand on theological issues.
A quiet, professorial type who relaxes by playing the piano, the first German pope for some 1,000 years and the second non-Italian in a row has managed to show the world the gentle side of the man who was the Vatican's chief doctrinal enforcer for nearly a quarter of a century.
But two weeks ago he showed his resolve again, warning rebellious priests that he would not tolerate disobedience on fundamental teachings such as compulsory celibacy and a ban on female priests.
His papacy has been hounded most by the child sex abuse scandals. He has apologized to victims several times for the criminal behavior of priests years before his election but victims' groups say he has still not done enough to make bishops accountable.
(Editing by Tim Pearce)