After four problem-free days, police prepared for a surge in street protests and demonstrations as the Democratic National Convention (search) winds to a conclusion.

Demonstrators typically look for the largest possible audience, said Boston Police Commissioner Kathleen O'Toole, and that's what they'll have Thursday.

"We suspect that will be the big day," O'Toole said.

Police tactical teams will be out in force, she added, as they have been throughout the week.

The Boston-area Bl(A)ck Tea Society (search ), an ad hoc group of self-described anarchists and anti-authority activists that formed a year ago to stage protests at the convention, called for "decentralized direct action" Thursday.

The group does not advocate violence but encourages demonstrators to hold street protests regardless of whether they have secured permits from the city.

"We know nothing of exact plans," said a man who identified himself as Matt Kerry, a volunteer at the group's temporary headquarters in the city's Back Bay section. "We have advocated that people take part in actions that are not permitted and not going through the official channels."

The group's members often go only by their first names or pseudonyms and hide their faces during protests to avoid being identified in photographs.

A direct action could be "anything from street theater to who knows," said Kerry. "There most likely will be arrests. Who knows how many. At any demonstration there's an arrest or two."

As of Wednesday night, police had made just one convention-related arrest, said spokesman David Estrada. The man, who was allegedly intoxicated, was not a protester and was arrested Wednesday evening near City Hall for disorderly conduct, Estrada said.

The biggest protests surrounding the convention were Sunday. About 2,000 anti-war activists and a separate group of 1,000 abortion opponents crossed paths briefly as they marched to the FleetCenter (search ) when convention delegates were arriving in town.

The next day police revoked abortion opponents' permit to demonstrate in front of Democratic presidential candidate John Kerry's Beacon Hill home, a decision later upheld by a federal judge.

The local chapter of the National Lawyers Guild (search ) said it will help any protester who is arrested and needs representation. Before the convention, authorities said they were preparing for more than 2,000 arrests.

Charles Shaw, 34, a Green Party (search ) activist from Chicago who has helped organize protest marches for various groups, said he did not anticipate problems.

"Creative demonstration is cool, but this implication that you need to take it up a notch is uncalled for," Shaw said. "The Boston police haven't warranted it. They've been nothing but professional."