A Manhattan judge has halted most of New York University’s sweeping expansion plan, finding that NYU needs approval from the state Legislature to build on public park land.

The ruling is a victory for a group of neighborhood activists who filed an Article 78 petition, Glick v. Harvey, 103844/12, challenging the city’s approval of NYU’s plan, which calls for the construction of four large new buildings over the next 20 years.

Manhattan Supreme Court Justice Donna Mills (See Profile) ruled Tuesday that NYU’s plan, which involves building on four parcels that are currently being used as parks, violated the public trust doctrine.

The parcels are officially designated as unused streets, not parks. However, Mills ruled that three of the parcels have been “impliedly” dedicated as park land. The fourth, a dog run next to NYU’s gym where the university wants to erect a new academic building, is not park land, she ruled. Mills also dismissed the petitioners’ challenges to the plan on various other grounds.

NYU spokesman John Beckman said the ruling “allows us to move forward with our first planned project—the facility to provide new academic space on the site of our current gym.”

However, Gibson Dunn partner Randy Mastro, who represents the petitioners, said that the city had approved the plan as a whole, and NYU could not go forward with only parts of it without going through the approval again.

“It is fanciful for anyone to spin that parts of this comprehensive project, which was approved as a whole and reviewed for environmental impacts on that basis, could still now somehow go forward without starting from scratch,” he said in an email.

Beckman said that NYU and the city were considering an appeal.

NYU is represented by Alan Levine of Cooley.