An unprecedented number of video cameras will be trained on Boston during the Democratic National Convention, with Boston police installing some 30 cameras near the FleetCenter, the Coast Guard using infrared devices and night-vision cameras in the harbor, and dozens of pieces of surveillance equipment mounted on downtown buildings to monitor crowds for terrorists, unruly demonstrators, and ordinary street crime.

For the first time, 75 high-tech video cameras operated by the federal government will be linked into a surveillance network to monitor the Central Artery, City Hall Plaza, the FleetCenter, and other sensitive sites. Their feeds from cameras mounted on various downtown buildings will be piped to monitoring stations in the Boston area and in Washington, D.C., and officials will be able to zoom in from their work stations to gather details of facial descriptions or read license plates.

With Boston Harbor just a few steps from the arena, the Coast Guard will be using its new ''hawkeye system" -- in place in one other port in the nation -- to watch area waterways. The network of infrared imaging, radar, and cameras that operate in both day and night conditions will give security officials a real-time picture of the harbor, and provide agencies an early warning if an unexpected ship enters area waters.

An unspecified number of State Police cameras are also being installed, and more than 100 previously existing MBTA cameras will be used to monitor area subway and bus stations. Law enforcement officials will have as-needed access to as many as 900 cameras that have been operated for months or years by the Massachusetts Port Authority, the state Highway Department, and the Big Dig.

Civil libertarians warn that the latest technology will be used to scare away protesters and others exercising their rights under the First Amendment. The critics complain that there are few state and federal laws regulating the use of video surveillance in public places.

''What this demonstrates is that '1984' is now technologically possible," said Barry Steinhardt, director of the American Civil Liberties Union's Technology and Liberty Program, referring to George Orwell's vision of an all-seeing totalitarian state. ''This is really a situation where we are really being asked to blindly trust the government. There is no oversight of this. There are no safeguards."

While video surveillance has become a common tool for police and private security personnel, Boston police and federal officials concede that the additional cameras and new technology represent another chapter in Boston. And it's here to stay: Boston police say the 30 or so cameras installed for the convention will be used throughout the city once the event is over.

''We own them now," said police Superintendent Robert Dunford. ''We're certainly not going to put them in a closet."

The Boston Police Department has a new policy permitting police to videotape political demonstrations during the convention, and federal officials also are planning to use hand-held cameras to videotape clashes between protesters and police.

Dunford, the department's top convention security planner, said Boston's new videotaping policy has safeguards against abuse. It mandates quick destruction of any tapes of demonstrations that do not show criminal activity.

''The only thing we're interested in is criminal activity," Dunford said. ''We're not interested in anyone who is simply coming out to voice their concerns."

Federal surveillance will be used to identify suspicious activities or respond to emergencies, not to snoop on individuals, said Ronald Libby, New England regional director for Federal Protective Service, a division of the US Department of Homeland Security. ''Watching stuff real-time tells you, 'That doesn't look right,' and we can do something about it," Libby said. ''It doesn't make sense to take all these valuable resources and look at the guy on the corner smoking cigarettes."

The video surveillance is the latest development to surface in the extensive $50 million security effort for the first national political convention since the Sept. 11, 2001, attacks. The Globe reported July 11 that an estimated 3,000 local, state, and federal law enforcement officers will police the convention. About 40 miles of roadway leading to the FleetCenter will be closed for part of the day during the event, which starts July 26.

Throughout the convention, police and other security officials on the ground will be in constant contact with those monitoring camera feeds back at command centers. The federal cameras will be linked into one network overseen by the Homeland Security Department and, while no similar central monitoring will exist for all of the city, state, and local cameras, officials from those various agencies have made provisions to share camera shots when necessary.

Live digital video from the State Police's new high-resolution, helicopter-mounted camera will be sent to the Multi-Agency Command Center, where law enforcement agencies will be coordinating their efforts. Boston, MBTA, and Coast Guard camera feeds will go to the command center. Several RV-sized mobile command vehicles also will tap into portions of the camera network.

On the water, the ''hawkeye" technology is a vast improvement over the Coast Guard's old monitoring system, which relied heavily on what its vessels in the water were able to detect, said Andrew Shinn, a Coast Guard spokesman and petty officer. ''Now we have eyes everywhere," Shinn said.

The Massachusetts Bay Transportation Authority has upgraded its cameras over the last several years, and now has cameras monitoring the interior and exterior of its stations, in a central network. While mindful of privacy concerns, MBTA Police Chief Joseph Carter said commuters should know that the T is a public system, ''and you are being watched."

''It is an integral part of our security tool kit," Carter said. ''We don't have any cameras in bathrooms and the message is not 'Hello, you're on Candid Camera.' But we have to enhance the safety and security of the public."

John Reinstein, legal director for the ACLU of Massachusetts, said that while individual cameras are not necessarily a problem, larger networks of them could be.

''If you network a sufficient number of them, then you get into evesdropping mode," Reinstein said. ''That would be chilling. But the more serious problems are the monitoring of political activity and the extent to which video surveillance is tied into other things like permanent record-keeping or facial recognition technology or both."

The idea of large camera networks has met resistance elsewhere in the country. A recent bid by the District of Columbia police to create a seamless, city-wide network of federal, district-owned, and privately operated cameras was met with resistance by the City Council, which deemed it too invasive.

Such a network would be feasible in downtown Boston, specialists said, since the city already has hundreds of public cameras and thousands of privately owned ones. A reporter touring a possible walking route from the Seaport Hotel on the South Boston waterfront to the FleetCenter found that a person's image could be captured by at least 33 cameras on public and private buildings.

Members of the public interviewed near the convention site Friday -- under the watchful eye of up to six cameras mounted on the FleetCenter and the adjacent Thomas P. O'Neill Federal Building -- had mixed responses to the news of the surveillance.

''I definitely think it's good for safety reasons," said Chris Bellomo, a 55-year-old teacher from Cheshire, Conn. ''I feel more comfortable [knowing] that, if something bad happens, more people are going to be watching and aware of it, and that help will be there if it is needed."

But the Rev. Ramon Aymerich, an Episcopal priest from Lowell, said the idea made him uncomfortable, since the poor, immigrants, those espousing politically unpopular causes would be singled out.

He said it reminded him of the time when he was a Catholic seminarian in Buffalo. ''I finally got over the idea of God as an all-present Big Brother, watching everything you do," he said. ''But now we have the government playing the almighty and omnipresent, and watching over us every second."