San Francisco -- Anti-war protesters in San Francisco got their first taste of a newly stiffened police response early Friday when they marched to Bechtel Corp.'s headquarters, expecting the same light opposition they got the day before.

Led by a little brass band, about 150 demonstrators laughed and chanted slogans as they rounded the corner of Beale Street off Market Street at 8 a.m. -- and quickly found themselves facing about 100 grim-faced cops in riot helmets, truncheons at the ready.

It was immediately clear that this was not going to be like Thursday, when hundreds of shouting protesters blocked Bechtel's doors all morning, with police mostly just standing by and watching vigilantly.

Friday, cops moved quickly to scatter the crowd, arrest the inner core and clear the street -- all within about a half-hour. It was too fast, according to miffed protesters, but just business as usual, according to the cops shoving them along the road.

"It certainly is zero tolerance today," said Deputy Chief Rick Bruce. "We're moving a little quicker."

The activists noticed the difference.

"They are definitely more aggressive today," complained Van Jones, an attorney with the group Bay Area PoliceWatch. "They gave us inadequate time to disperse, and they violated their own department's policy."

Other demonstrators noticed the change later in the day, too.

Around 1 p.m., hundreds of police officers prevented protesters from joining a rally at a plaza on New Montgomery Street by barricading the street - - as well as the sidewalk.

"I feel like they're tactically keeping us from peaceful assembly," said Chantal Kovash, an elementary-school teacher from Marin.

Police Sgt. Felix Bilbao, working the Bechtel protest, shook his head emphatically when asked if he had urged his men to move faster on the crowds Friday.

"I don't think there's anything different about what we're doing today," he said, as a bus full of arrested protesters was taken away. "Our job is to clear the street, and that's what we did."

That's exactly what business leaders wanted after Thursday's roving protests left Market Street and other major thoroughfares blocked for much of the day.

Lee Blitch, president and CEO of the San Francisco Chamber of Commerce, called Mayor Willie Brown's office Thursday hoping for police to do more to control protesters who stopped traffic, vandalized businesses and prevented people from going to work. The business group heard from several members who voiced concerns -- "and I expressed that to the mayor's office," Blitch said.

He said he had spoken to Eleanor Johns, Brown's chief of staff.

"I said we had a couple of hot spots, and we would appreciate police response," Blitch said. "They were glueing ATMs, throwing things through windows -- really doing things that hurt the public."

Blitch said Johns had spoken to police brass, and everyone ''was very responsive."

Brown sounded surprised when it was suggested that police had toughened their response, noting that officers made some 1,400 arrests Thursday.

But if police did indeed have a new approach Friday, Brown said, it wasn't a decision he was in on.

Assistant Police Chief Alex Fagan and his command staff "are running the show," Brown said. "I don't think their approach is any different. The situation keeps changing and they're responding as needed."

Ken Cleaveland of the Building Owners and Managers Association, a commercial real estate trade group in San Francisco, said he detected a different attitude by police Friday.

"We didn't call the mayor," he said, "but we're glad to see it."

Chronicle staff writers Joe Garofoli, Kathleen Sullivan and Nanette Asimov contributed to this report. / E-mail the writers at rgordon@sfchronicle.com and kfagan@sfchronicle.com.