LOS ANGELES — Hollywood studios said Thursday they will file hundreds of lawsuits later this month against individuals who swap pirated copies of movies over the Internet.

The move is a reversal of the studios' earlier reluctance to follow the aggressive legal path taken by the music industry. Internet piracy of movies is not nearly as rampant as in the music industry, largely because huge movie files can take hours to download, in contrast to less than a minute for most songs.

But Dan Glickman, the new head of the Motion Picture Association of America, said the lawsuits were necessary now, before high-speed Internet access makes downloading pirated copies of movies easier.

"This was not an easy decision, but it must be done now before illegal online file sharing of movies spins out of control," Glickman said Thursday.

The legal action also clears the way for movie downloading businesses that are supported by the studios.

The MPAA claims the U.S. movie industry loses more than $3 billion US annually in potential revenue because of physical piracy, or bogus copies of videos and DVDs of its films.

Videotaped copies of films in theatres often are digitized or burned on DVDs and then distributed on file-sharing networks accessed with software programs like eDonkey, Kazaa and Grokster.

Glickman did not say how many lawsuits would be filed, although sources who spoke on condition of anonymity said several hundred individuals would be named in the first round. Glickman said the legal campaign would be ongoing.

The lawsuits would seek civil penalties of as much as $30,000 per download and as much as $150,000 if the infringement is proven to be wilful.

Some critics of the music industry's legal efforts question whether they are effective. They also question the negative backlash that comes from suing people who may have downloaded one or two songs.

"The recording industry lawsuits don't appear to have reduced file sharing to any meaningful degree," said Fred von Lohmann, a senior intellectual property attorney with the Electronic Frontier Foundation.

The lawsuits will be accompanied by an ad campaign featuring a photo of a finger on a computer mouse and the obscured screen names of people the MPAA says are breaking the law.

"Is this you?" the ad reads. "If you think you can get away with illegally trafficking in movies, think again."

The MPAA, which represents the seven major film studios, has tried several methods over the past few years to stem illegal downloading, including ads that play in theatres emphasizing how piracy hurts set painters, directors, electricians and others who earn their living in the movie industry.

The MPAA has also been aggressively pushing for new laws and stiff penalties against people who sneak camcorders into theatres to make illegal copies of films.

The decision was also made in part to protect several nascent legal movie downloading businesses, the MPAA said.

Five studios formed an Internet service called Movielink two years ago. Lions Gate, among other investors, offers Internet streaming and downloading of films through CinemaNow. And The Walt Disney Co. is testing a service called MovieBeam that delivers films over existing broadcast television spectrum.

But the Web-based services have yet to catch on because they only deliver movies to computers, while most people prefer to watch films on their television sets.

Legitimate services also only offer movies long after they have left theatres and even after the time they are available in video rental stores, while online music services such as Apple's iTunes offer many songs the day an album hits stores.

Backers of legal alternatives to online movie piracy say legal action is necessary now for their services to thrive and to begin offering more options, including the ability to burn DVDs and watch movies earlier.

"There is no question that as movies come on to peer-to-peer sites, our business is harmed," said Jim Ramo, chief executive of Movielink.

Ramo said more aggressive advertising of his and similar services isn't appropriate now, when only 30 per cent of homes have broadband Internet access and most of those connections are to computers.

"Pirates are getting movies on PCs and seem to be willing to watch them on PCs," he said. "We are well known within the community that is interested in downloading movies on PCs. It's just that's not as big a market as the cable television market."