Images of police dousing students with pepper spray at UC Davis and jabbing them with batons at UC Berkeley drew national condemnation and set off new protests Monday, as UC's president urged chancellors across the state to protect students' right to protest peacefully.

The confrontations have led to soul-searching across the UC system and calls for UC Davis' chancellor to resign, extraordinary developments at college campuses that pride themselves on a history of activism and political dissent.

"We cannot let this happen again," UC President Mark Yudof said, after convening chancellors to discuss the use of police force, which gained national attention after video of an officer pepper spraying a row of sitting students, their arms locked in peaceful resistance, spread across the Web.

At a rally at UC Davis, Chancellor Linda Katehi took the stage and said, "I'm here to apologize" for the pepper spraying. "I really feel horrible for what happened on Friday."

She spoke only briefly, then students shouted at her to step down. A petition calling for her resignation had received more than 70,000 online signatures by Monday afternoon. By 5 p.m., students returned to the quad and began erecting a dozen tents to restore the Occupy encampment.

Police force galvanized further protests at some UC campuses Monday and has been criticized in a range of forums such as "The Colbert Report" and Forbes.com. Angry UC

Protests over the past two weeks -- aligned with both the Occupy Wall Street movement and criticism of UC's escalating education costs -- have resulted in the arrest of more than 60 students statewide.

The national council of the American Association of University Professors issued a statement Monday condemning the violent tactics. "All universities must make space for political dissent," the statement read. Students and faculty members must be free "to engage in nonviolent civil disobedience without fear of bodily harm arising from a violent administration response."

As UC officials investigate Friday's pepper spraying of 11 students -- two of whom were treated at a hospital -- the campus police chief and two officers have been placed on leave.

In an interview on KQED, Katehi said the officers "were not supposed to use force; it was never called for. They were not supposed to limit the students from having the rally, from congregating to express their anger and frustration."

At Monday's rally, students described being paralyzed with fear and feeling a sting "like hot glass."

"I had my arms around my girlfriend. I just kissed her on the forehead and then he sprayed us," said mechanical engineering student David Buscho, 22, of San Rafael. "Immediately we were blinded. ... He just sprayed us again and again and we were completely powerless to do anything."

Harsh tactics also were used this month at UC Berkeley, a university proud of its history of activism, when police struck protesters with batons and dragged them by the hair to break up a tent city.

Faculty members say that many options are available besides violence.

"To begin with, the chancellor could have thanked them for their sense of civic duty," said UC Davis music professor

"Just imagine if instead of carrying assault rifles, batons, body armor, face shields and spray canisters, the cops arrived in slacks and sweatshirts? What if they brought milk and cookies? What if they decided to do nothing? Nobody would have known it was a protest," he said.

Until recently, police have taken a hands-off approach to campus protests, sobered by the Kent State killings during the Vietnam War. There have been many demonstrations at UC campuses -- against nuclear energy, nuclear weapons, CIA involvement in El Salvador, oppression in South Africa, military recruiting and the Iraq wars -- but no pepper spray or batons.

"Linking arms is an iconic image of nonviolent civil disobedience, the best way to de-escalate any confrontation," said Ostertag, who said the most serious consequence was expulsion.

The recent incidents represent an escalation of police violence, said Norm Stamper, the police chief who oversaw Seattle's crackdown on protesters during the World Trade Organization protests in 1999.

Since then he has acknowledged the mistake of that tough approach and decries what he calls "the militarization of police. It is all too easy to resort to weapons that ought not be used at all, or in last-resort situations. I find the decision to use chemical agents on campus very disturbing."

At Stanford University, police officers can carry pepper spray, according to spokeswoman Lisa Lapin, but the university follows protocol of the Santa Clara County Sheriff's Office, which states that use of chemical agents on nonviolent protesters is not authorized.

UC Santa Cruz policy states that "an officer, given the circumstances perceived by him or her at the time of the incident, is permitted to use only that amount of force that reasonably appears necessary to bring an incident under control."

Reaction to the UC police actions has been harsh across the country, including at Duke University, where students traditionally set up tents for weeks and camp outside for coveted basketball tickets.

"Our students face a difficult future," said Duke professor Cathy N. Davidson, who has written extensively about the future of education. "This should not be a time to beat them up."

The Associated Press contributed to this report. Contact Lisa M. Krieger at 408-920-5565.