MONTREAL - Divisions in Quebec's protest movement erupted into public view Tuesday, with masked demonstrators disrupting a news conference held by the province's more moderate student groups.

The bizarre scene, featuring black-clad anonymous spectators heckling the student leaders, raised new questions about whether the Charest government can ever negotiate a satisfactory settlement that would end weeks of unrest.

Hours after the news conference, a previously scheduled May Day march featured scenes Montrealers have become familiar with: smashed windows, objects tossed at police, and officers responding with chemical irritants, rubber bullets and billy clubs. More than 100 people were arrested and one protester was injured.

Meanwhile, student protestors still went ahead with another in their series of evening demonstrations. For the most part it was peaceful, although there were several arrests and the number of students was smaller than usual. Montreal police reported at least two people were arrested, which included a man who was charged with assaulting a police officer.

On a number of occasions in recent days, student protesters have in fact made clear their impatience with the masked vandals in their midst; they have delivered admonitions and Bronx cheers at demonstrations whenever the minority in the crowd starts causing damage.

On Tuesday, at a formal news conference, people in masks were suddenly shouting back.

The government was quick to seize on signs of discord at the news conference, including the heckling and the fact that one of the main student groups was absent.

"This illustrates that the student movement is not monolithic," said Education Minister Line Beauchamp. "Frankly, it's getting a little hard to follow."

The two student leaders holding the news conference were trying to release a series of proposals to the government, aimed at resolving a weeks-long dispute over tuition.

Even before their so-called "counter-offer" was made, it was already doomed. The seven-point plan included a proposal for a tuition freeze, something the Charest government has repeatedly called a non-starter. The rejection from Beauchamp was swift and adamant Tuesday.

But even that offer -- the one deemed unacceptable by the government -- did not go far enough, according to the small group that crashed the event.

The masked protesters repeatedly heckled the student leaders and at one point forced an interruption of the news conference.

"(Your) counter-offer: (It's) mud and crumbs," said one large banner held up by the news conference-crashers in the back of the room.

The third main student federation, the most hardline one -- called the C.L.A.S.S.E. -- will be tabling its own proposals later this week.

There's no evidence Tuesday's event-crashers were formally affiliated with any official student group. However, one of the masked demonstrators said, without revealing his identity, that he was represented by the C.L.A.S.S.E. federation.

There have been heated disputes at recent demonstration marches in Montreal, over how radical to get and over whether to allow a so-called "diversity" of protest tactics, like vandalism.

Window-smashers and other vandals have been booed and shoved aside by more peaceful demonstrators who believe the key to success for their cause is remaining calm and winning public sympathy -- which they say is undermined by the association with vandalism.

The proposals released Tuesday by the two student federations called for:

--A committee to monitor management of universities

--A limit, to three per cent, of university expenses that are peripheral to education

--An analysis of arrangements between businesses and universities, when it comes to patents

--A two-year moratorium on university funding increases

--A five-year moratorium on construction of new campuses

--An estates-general, or roving consultations, on education

--A freeze on tuition at 2012 level

Later in the day, scuffles began in the street between police and the forces of anti-capitalism. The May Day march was described on the website of one group as part of a more ambitious plan.

"We call for an unlimited general strike, because we do not want to be the oil that drives the gears of capitalism," said the website for that group, the Convergence of Anti-Capitalist Struggles.

"We will be the iron bar that will derail it!"

Protesters threw chunks of asphalt, bottles and sticks at police. They also mocked police by dangling donuts in front of them, off of makeshift fishing rods. At least a half-dozen windows were smashed at one bank on Ste-Catherine Street.

Police responded by pumping chemical irritants into the crowd and used riot gear to try dispersing the protesters -- a reaction some marchers called excessive.

Many people at the march expressed support for the student cause. They included Lydia Lamontagne, a 34-year-old Montreal CEGEP professor who has taught at the universities of Guelph, Ottawa and Prince Edward Island.

She said most teachers are behind the student protesters. Lamontagne said she doesn't want education to become more expensive, as it is in other places in Canada.

"Professors support free education for everyone and the accessibility is really what's involved here," she said.

"It's not about the amount of $325 a year -- it's for the idea that everybody should have access to university no matter what level they come from.

"(I) know from my experience in English Canada that (in) different programs that are more expensive like medicine or law, it's mostly people that come from a higher income and that's really what we don't want in Quebec... We created a society where everybody is able to go to school."