Pope John Paul II asked people to pray for the town of Bethlehem on Monday, just hours after an incursion by Israeli tanks.

The pontiff appeared in the window of his study high above St. Peter's Square at noon on the day after Easter. He told the faithful gathered below of his ``apprehension and pain'' and said Bethlehem was ``in great danger.''

Israeli tanks rumbled into Bethlehem and other West Bank towns at sunrise on Monday, widening an operation Israel says is aimed at ending attacks by suicide bombers. A few hours later, they pulled back to Bethlehem's outskirts.

Witnesses said the tanks stopped about 500 yards from the Church of the Nativity, built over the traditional birthplace of Jesus.

Violence in the Holy Land has preoccupied John Paul this Easter. On Sunday, he dedicated much of his traditional ``Urbi et Orbi'' (to the city and to the world) to Mideast violence. He denounced the ``horror'' of the violence and pleaded with the Israelis and Palestinians to seek peace.

Assisted by two cardinals, the frail, 81-year-old pope celebrated Easter Mass on the steps of St. Peter's Basilica.

It was something of a comeback for John Paul, who was forced to give up several Holy Week traditions in the preceding week because of a painful knee. He let other clerics stand in for him at the altar on Palm Sunday and Holy Thursday Masses and watched rather than walked the Good Friday procession at the Colosseum.

The Vatican has said the pope has arthrosis, a joint disease involving destruction of cartilage. A Rome surgeon said Sunday that the Vatican is considering knee surgery.

The pope appeared to grimace in pain Sunday, his left hand shook as he rested it on the altar and he clenched a book stand for extra support.

His voice was sometimes slurred, a symptom of Parkinson's disease. But at the end of the 90-minute Mass, the pope summoned his strength to raise his voice against Middle East bloodshed.

Speaking in Italian, he called on Christians everywhere to work to help stop ``the dramatic spiral of imposition of will by force and killings which bloody the Holy Land, plunged again in these very days into horror and despair.''

He said it appeared that ``war has been declared on peace'' and called on political and religious leaders to do what they can to foster peace talks. ``Nothing is resolved through reprisal and retaliation,'' the pope said.

John Paul also lamented conflicts elsewhere in the world, saying peace ``is often a precarious balance of powers that soon or later turn against one another once more.''

Surgeon Alfredo Carfagni at San Carlo di Nancy hospital said Sunday that the hospital was on alert, waiting for the Vatican to decide whether the pontiff would have his knee examined there to see if surgery should be performed.

There was no word Monday from the Vatican about the surgery.