SAN FRANCISCO, JULY 6 -- Five people were arrested today as the city began enforcing a ban on sleeping in parks in an effort to empty a downtown plaza where more than 200 homeless people have camped for two years.

As an alternative to arrest for violating the public sleeping ban, police offered vouchers for admittance to two new city shelters. Thursday evening, a group of 50 activists and homeless people at the Civic Center decided to accept the city's offer. The group noisily marched seven blocks to one of two new shelters, where a worker told them all the rooms were filled.

City officials said the homeless could obtain vouchers for free shelter elsewhere, but the group returned to the plaza -- a park surrounded mostly by government buildings.

"There's no room," said a homeless woman, Lima Rashida. "We have no place to go but back to the Civic Center."

Police had been under orders to begin making arrests at midnight, but after the homeless marchers were faced with no shelter space, officers did not immediately intervene.

Of the five people arrested later, three were booked on misdemeanor counts of illegal lodging and interfering with police and two were cited with illegal distribution of food, police said.

The march came after a peaceful candlelight vigil mourning the death of Mitch Snyder, an activist for the homeless in the District, who was found hanged Thursday in what police said was an apparent suicide.