Snarling traffic across the Italian capital, hundreds of thousands of pilgrims descended on St. Peters' Square Saturday in what was seen as a dress rehearsal for the huge crowds expected in 2000, the church's holy year.

Police said some 250,000 Catholics from around the world had reached the square by early evening for a religious vigil.Pope John Paul II greeted the cheering throng as he glided aboard his "popemobile" along a passageway kept open by police.

But for ordinary Rome residents, many streets were off-limits. And many found notices stuffed in their mailboxes urging them to stay home.

Traffic was barred from neighborhoods near the Vatican, and backups were reported along nearby roads. Cars on the beltway around the capital found the going slow.

About 2,000 chartered buses, as well as specially reserved trains, brought participants to the capital, where they jammed sidewalks, subways and city buses to reach the square.

At least 20 million extra tourists and pilgrims are expected throughout 2000 for celebrations marking the start of the church's third millennium.

Some observers were quick to predict disaster in 2000.

"Curfews in entire neighborhoods, buses which immobilized the Tiber-side road, appeals not to go out or to do so without cars are things which speak for themselves," said Giovanni Negri, a member of the group Lay Observer of the Jubilee. He said the group was considering going to court to protect citizens' rights to free movement.

Negri cited the case of a Roman who had to prove to police he lived near the Vatican in order to reach his home after going out to buy bread.