With little more than two weeks left before the Republican National Convention, organizers of a massive antiwar march have backed away from an agreement to hold the rally on Manhattan's far West Side, setting the stage for a showdown with the Bloomberg administration.

The march and rally are widely expected to draw more than 250,000 people on the convention's eve. But United for Peace and Justice, the group organizing the march, announced Tuesday that it has decided to fight again for a rally spot in Central Park.

"Exiling a rally to a remote sun-baked highway makes a mockery of the constitutionally protected right to assemble," said Leslie Cagan, the group's national coordinator.

Meanwhile, city officials faced headaches on another front, as city firefighters and police officers refused to rule out a strike or sickouts during the convention. The uniformed services argue that they deserve bigger raises than other city workers because they risk their lives daily. City officials say they have offered more money, for money-saving labor concessions.

Parks Department officials have refused to budge on the site of the demonstration. In a written statement, the Parks Department denied the protest group's latest request "for the same reasons stated in the denial of your earlier application." Parks Commissioner Adrian Benepe has said that large numbers of protesters trampling the grass would cause irreparable harm to Central Park's Great Lawn. Activists sought to answer this criticism by offering to use three sites within the park, rather than concentrate in one meadow.

"They can't just rubber-stamp" the rejection, said Bill Dobbs, spokesman for United for Peace and Justice. "It's clear they didn't even consider this application seriously, because . . . it's entirely different."

Republican Mayor Michael R. Bloomberg issued a written statement Tuesday calling on organizers to concentrate on the permitted route and "stop the theatrics."

The city's refusal of a Central Park rally permit has rankled antiwar activists and civil libertarians, who say the park has great symbolic import and functions as the city's unofficial "town square." The activists decided to revisit the question after news reports in the past two weeks revealed that the park's refurbished grass was designed to withstand hard use. Parks officials have granted permission for smaller groups, including some Republicans, to use the park during the convention.

A recent public opinion poll conducted by Quinnipiac University found that most New Yorkers support a rally in the park.

Cagan, the protest group's national coordinator, also noted that the alternative site, along the West Side Highway just north of Ground Zero, is problematic. The group is worried about the heat and water supplies in an area that offers no shade. "Our medical people have advised us against taking people into this area," Cagan said.

City officials have declined to pay for water, saying the city cannot subsidize protest. Critics noted that Bloomberg contributed an estimated $7 million to the convention.

Staff writer Michael Powell contributed to this report.