NEWPORT, R.I. (AP) — A proposal to build a visitors center on the grounds of The Breakers, the Gilded Age Vanderbilt family mansion and national historic landmark, is dividing Newport’s preservationists, neighbors, and even some family members in a seaside city where tourism is its lifeblood.

The Preservation Society of Newport County, the nonprofit group that owns the 70-room mansion, says the center is badly needed to serve The Breakers’ 400,000 annual visitors. Many opponents agree something is needed, but they want it across the street in the parking lot or elsewhere, not on the 13-acre grounds of the property, which they say would be irreparably damaged.

During the months since the $4.2 million plan was released, then rejected by the city’s Historic District Commission, the disagreement has devolved into a bitter fight, with opponents who once considered themselves allies of the Preservation Society now accusing it of steamrolling or cutting people out when they disagree. The Preservation Society says it has explored the alternatives, and its plan is the only feasible one to protect the magnificent home built by railroad magnate Cornelius Vanderbilt II.

“We have hired the best people, the brightest people. They’re very sensitive to the issues. There is no steamroller. We believe we’re doing the right thing,” said Don Ross, chairman of the group’s board.

Both sides say they’re fighting for the future. Opponents set up a “Save the Breakers” Facebook page in August. The Preservation Society set up a competing page the next day, also called “Save the Breakers.”

On Friday, the National Park Service weighed in, siding with critics and asking the Preservation Society to reconsider a plan it said could damage the national historic landmark.

The Preservation Society will go before the city’s zoning board on Monday to appeal, and says if it’s again turned down, it will go to court. In the meantime, the plan has drawn some high-profile detractors, including designer Gloria Vanderbilt, who in a letter to the editor of Newport This Week last summer decried the possibility that visitors to the “magical kingdom” her grandfather built would be greeted by “plastic, shrink-wrapped sandwiches.”

The Preservation Society acknowledges some Vanderbilts are angry, but says others privately support the idea once they hear more about it.

The Breakers, named for the breaking Atlantic waves it overlooks, is one of the most popular historic house museums in the United States. The estate opened in in 1895, during a time when Newport functioned as the nation’s summer social capital, and became the crown jewel in a city populated by mansions.

By the middle of the 20th century, though, many of the once-splendid homes had fallen into disrepair. Some were razed. The Preservation Society was formed to save some of those buildings. It purchased The Breakers from Vanderbilt’s descendants in the 1970s and today owns 11 properties that collectively receive more than 900,000 visitors annually.

Those who visit The Breakers today must either pay admission at a small ticket booth or at a tent erected on the grounds during warmer months. Restrooms are in the basement or in portable toilets outside. Snacks are available from vending machines situated in an outdoor shed.

The Preservation Society’s plan calls for a 3,700-square-foot building reminiscent of a conservatory to be built inside a grove of trees, where it says it would not be visible from the house or street. It would include ticketing for The Breakers and other of its houses, as well accessible restrooms. It would offer a place to get out of the weather as well as a place to buy sandwiches and sit.

Opponents ask why it can’t simply be built across the street, where it would be close by while not disrupting the original plan of the estate’s designers, including architect Richard Morris Hunt, forester James Bowditch and his brother, landscape engineer Ernest Bowditch, who was a student of Central Park designer Frederick Law Olmsted.

The Preservation Society says the building would take up too many parking spaces, forcing more traffic into the neighborhood, which includes several other large residences, Salve Regina University, and an entrance to the Cliff Walk, itself an attraction that draws hundreds of thousands of visitors annually. It also says building it in the lot would be too far from the house and could be seen from the street.

“That’s nonsense,” said Don Christ, chairman of the board of the Alletta Morris McBean Charitable Trust, which has given more than $10 million to the Preservation Society over the years and is among its largest donors. He calls the current plan inappropriate and says he doesn’t understand why a group that stands for preservation is pushing it.

He also objects that the group plans to spend so much on the project when there are other preservation projects at The Breakers that could use the money.

“If you go through The Breakers, it’s in woeful shape,” he said. “They overuse it because it’s the heart that pumps money through the Preservation Society.”

Among the plan’s supporters, however, are the state’s top economic development official, the local chamber of commerce and tourism officials. Rhode Island had an unemployment rate of 9.1 percent in December, but tourism is one of the state’s few economic bright spots.

Ronald Onorato, a Newport resident and University of Rhode Island professor who has published several books on Newport architecture, sits on a state preservation board that was asked to weigh in on part of the project. He voted yes. He says there is a tug-of-war in the neighborhood as more tourists have poured in. The Breakers is now a museum and must be run that way, rather than as a private house, he said.

But in its letter to the Preservation Society on Friday, the National Park Service pointed out that several historic homes have visitors centers set back from the main attraction, including Monticello. The group’s plan, the park service wrote, “constitutes a significant and intrusive change.”