Mayor Bloomberg expressed his surprise yesterday that the group organizing the largest protest planned for the Republican National Convention would “renege” on its deal with the city.

Speaking to reporters, the mayor said the group, United for Peace and Justice, had a recent meeting with police that he said went well, “to say the least.”

But he did not soften his stance on the group’s desire to get a permit to rally in Central Park.

“They’re not going to get a permit for a quarter of a million people in Central Park,” the mayor said. He said he worried about the grass and the underground irrigation system at the Great Lawn, as well as emergency vehicle access.

Protest organizers were incredulous.

“It makes one wonder whether a lawn museum in Central Park is going to be his legacy,” said a spokesman, William Dobbs.

The group’s conflict with the city dates back to anti-Iraq war protests in 2003. It flared up again Monday, when the group broke its agreement with the city to march around Madison Square Garden and then south on the West Side Highway. Organizers cited concerns about the health and safety of its marchers and a threatened drop in participation from member groups.

The group applied for a new permit to gather in three sites in Central Park, and was promptly rejected that same day. They are “mulling our options” and may file a grievance in federal court, or may conduct a highly rumored illegal march up Seventh Avenue to the park.

Yesterday a member group, the Not in Our Name Project, met near the Columbus fountain to demand a permitted march to the park, though they did not say what they would do if the city does not relent.

The mayor has offered myriad reasons for why the anti-war group could not gather in the park, but he has offered no such reasoning for why another group, the Act Now to Stop War & End Racism Coalition, could not hold its rally on the Great Lawn.

The group expects to file suit in federal court this week to hold a rally of 75,000 people. The crowd would be 10,000 fewer people than the one that attended the Dave Matthews concert sponsored by America Online in September 2003.

“There’s a lot more that goes into determining if a site is appropriate for a large group of people,’ said a Parks Department spokeswoman, Megan Sheekey. “There’s bond, the possibility of a rain date, ease of access.”