Frustrated by years of debate and now held up by a lawsuit, supporters of a $21 million Parks & Recreation Department renovation of Union Square Park’s north end are expressing dismay at delays in the plan.

Today a judge will decide whether to allow a lawsuit, which has halted construction at the site since last Monday, to proceed. At issue is a proposal to build a seasonal restaurant in the park’s historic pavilion as part of the renovation: The plaintiffs in the case argue that the pavilion should be used as a play space for children, noting an abundance of restaurants in the neighborhood and that the state Legislature should have to approve the use of city parkland for non-park purposes. City officials say the plan would triple the size of playground space in the park and point to the local community board’s support as evidence of its legitimacy with local residents.

Two former co-chairwomen of the Union Square Community Coalition and members of the local business improvement district’s Resident Advisory Board, Gail Fox and Susan Kramer, said yesterday that the dominance of the issue in recent years has upset them.

“We would hold a board meeting, and it would all be single-channel and it was very frustrating,” Ms. Fox, who said she resigned her position with the group in 2006 in large part because of the intense focus on the issue, said. “I just want to see a new playground up there.”

The USCC is now a plaintiff in the lawsuit, which Ms. Fox and Ms. Kramer oppose.

“I think it’s crazy that the lawsuit has started just as they have the shovel in the ground,” Ms. Kramer said. “By doing what they say is for their children, they are hurting the children by not letting this plan go forward and not letting children have a new playground.”

The president of another plaintiff in the case, NYC Park Advocates, Geoffrey Croft, said the lawsuit is a necessary step, as the city has ignored community opposition to the renovation.

“The city’s been told in countless meetings that nobody wants this thing,” he said. “It just seems like the more the community and electeds come out against it, the more the city digs in their heels.”

Adding playground space, which both advocates and opponents of the plan have said is a top priority, is the most crucial aspect of the renovation — not how the pavilion is ultimately used, said David Siesko, the chairman of Community Board 5, which includes the park.

“We are concerned that there’s a delay in the renovation of the playground,” Mr. Siesko said. “That is something that the community and the community board I think are anxious to get under way and completed, because that serves the local interest of families.”

If construction is allowed to continue, the city is expected to complete the renovation by the end of 2009.