Mayor Michael Bloomberg's administration wants to shrink the vendor population by up to 80 percent in some areas - dramatically altering a colorful part of the cityscape that has for decades served as an outdoor gallery popular among tourists in a city known worldwide for its arts.

"If they do this, it will be war in the city because so many people will lose money and a place to show their work," said Alex Basansky, a photographer who sells his prints of city scenes at the southeast entrance of Central Park.

The regulations would also severely limit the number of vendors in parts of Central Park, plus all of Union Square and Battery Park in downtown Manhattan and the High Line Park, a new elevated park along Manhattan's far West Side.

The Bloomberg administration says street art has outgrown its space in the city's most popular parks, dominating sidewalks and interfering with pedestrian traffic. Vendors say the rules violate their First Amendment guarantee of free expression.

"It's about balance," said Parks Commissioner Adrian Benepe. "They can still vend their stuff, they just can't do it in uncontrolled droves where park visitors are forced to walk through a gauntlet of vendors."

Vendors currently do not need city permits to sell what is called "expressive art," which includes writings and visual art like photographs, paintings and sculpture.

Officials say there are now more than 300 vendors in the four most busy parks, and seek to cut it down to 81.

The Parks Department is holding a hearing next week on the regulations. If the rules are passed, vendors say they will challenge them in federal court.

Renowned First Amendment attorney Martin Garbus, who has no connection to the case, said the artists likely have a good argument. He said the city would have to prove that vendors create a serious problem, like blocking a critical intersection, for example.

"You can't regulate them if all they do is sell peacefully," Garbus said.

In anticipation of the fight, vendors in the parks are displaying yellow signs saying "Stop Harassing the Artists" and "Artist Power."

One artist in Union Square created a mock old-West style poster, with a photo of Bloomberg, that read "Wanted: Killer of NYC Artists' Rights."

Under the regulations, 18 vendors would be allowed in Union Square. On a recent sunny weekday morning, more than 50 vendors had set up tables by 11 a.m.; on weekends, the number can reach 100.

The city says the relatively small park can get 200,000 visitors per day during the summer season.

"I'm very concerned - we're being driven out," said Ava Day, an oil painter who sells her landscapes for $10 to $25 at a table along 14th Street, the park's southern border.