By Ray Sanchez

NEW YORK (Reuters) - A standoff near Wall Street between anti-capitalism protesters and police may drag on into winter, with an unauthorized march on police headquarters the likely next test of whether tensions escalate.

Although experts don't expect the type of violence recently seen in London, protesters plan to shift their attention from bankers to police on Friday for a demonstration on the streets outside the police center of operations at One Police Plaza.

The Occupy Wall Street movement is adding complaints of excessive police force against protesters and police treatment of ethnic minorities and Muslims to its grievances list, which includes bank bailouts, foreclosures and high unemployment.

During the protests police have made about 100 arrests and used pepper spray, which they called a better alternative than night sticks to subdue those blocking traffic.

"We're here for the long haul," said Patrick Bruner, a protester and student at Skidmore College in upstate New York, who is among those camped out in a private park near One World Trade Center, the skyscraper rising at the site of the September 11, 2001 attacks.

In the British protests, more than 2,700 people were arrested after destruction and looting spread from London to other cities. Authorities said some rioters were known gang members.

In New York, the protesters are largely educated, organized and their marches are planned, rather than spontaneous.

After hundreds of protesters were denied access to some areas outside the New York Stock Exchange on September 17, demonstrators set up a rag-tag camp three blocks away.

Zuccotti Park is festooned with placards and anti-Wall Street slogans. People sleep wrapped in blankets or sleeping bags, some on donated mattresses. There is a makeshift kitchen and library and celebrities from filmmaker Michael Moore to actress Susan Sarandon have stopped by to show support.

Mindful of the cold New York weather coming, protesters have a "winterization committee" to prepare for the season.

Vancouver-based activist media group Adbusters organized the protest but failed to attract the throngs some hoped for. Instead, there are a few hundred people, mostly unemployed youth and college students.

"These are the most over-educated crowd of people that I've even seen in my life," said Daniel Levine, a student at Baruch College. "People come out of college and there are no jobs."

Friday's planned march comes less than a week after police arrested 80 people. A police commander used pepper spray on four women. A video of the incident was widely viewed on the Internet, inspiring many protesters who vow to continue their anti-capitalist protests indefinitely.

"They'll try to push the envelope further the next time," said police Deputy Inspector Roy Richter, president of the Captains Endowment Association, a police union.

International security expert Patricia DeGennaro, a senior fellow at the World Policy Institute and professor at New York University, said she doubted the Wall Street protests would turn violent.

"Americans have become too complacent with the way their society is being run," DeGennaro said.

(Editing by Daniel Trotta and Jerry Norton)