Ms. Moynihan, the daughter of the late U.S. senator from New York, Daniel Patrick Moynihan, was deep into lunch last Friday at Da Umberto, a classy Italian restaurant in Chelsea she chose because of its old European flair.

She was brought up partially in India—her dad was ambassador while she was in high school—and remains entranced by Southeast Asia. In fact, at age 50 and a single mother of a 16-year-old, she is studying for a master’s degree in international development at the New School in order to get a job with the United Nations and travel back, hopefully to Thailand. But something is keeping her here at least in the meantime—the angry New Yorker in her, and also the Moynihan in her.

After a varied life following Andy Warhol, marrying the son of Richard Avedon (and quickly divorcing after having one son) and writing short stories and screenplays, she opened another chapter when her father died four years ago: crusading for a new Penn Station to augment what Ms. Moynihan calls “the pit” underneath the Madison Square Garden arena.

She did this by starting an organization, Friends of Moynihan Station, to act as a cheerleading squad for an immense public works project that has dragged on for some 15 years and is still in the planning stages. Ms. Moynihan dates the genesis even further back, to the late 1980’s, when her father first adopted the idea of using the Farley Post Office, on Eighth Avenue between 31st and 33rd streets, as an extension of Penn Station, which is right across the street under Madison Square Garden.

Ms. Moynihan carries absolutely no power over what happens, but she has more moral authority than pretty much any other single player. Officially, everyone likes the idea of a better train station, but in reality, there are as many different opinions on this matter as there are agencies, companies and organizations that have stuck their noses into it. And since the Empire State Development Corporation, the state economic development agency, issued its first written outline of the project last month, those differences have become even more urgent to reconcile.

The state wants to keep the cost to taxpayers down. The mayor wants to wrench away a sui generis property tax exemption from his political nemesis, Madison Square Garden. The Garden, which would move to the rear of the Farley building, wants to put up signs and ticket kiosks outside or inside the old post office. Two nonprofit organizations, the Municipal Art Society and the Landmarks Conservancy, want to preserve as much of the Farley building’s 1913 interior as possible.

Ms. Moynihan seems to be leaning toward the developers The Related Companies and Vornado Realty Trust, at the expense of the preservationists, because, well, after 15 years on the drawing board, the project is in danger of getting dusty

“Preservation is an important component, but it is not the only component,” she said. “It’s a transportation project first and foremost. My concern is that we don’t get distracted by some elements of the project when we have the heavy lifting to do of the structural engineering that’s going to have to take place to improve the disaster, the nightmare, the insult that is the pit—otherwise known as Penn Station.”

Her way of speaking is to assume that you share her sympathies immediately, so that she enlists you instantly on a ride of enthusiasm, rage, disbelief and hope through a full spectrum of issues: the Chinese occupation of Tibet, the Bush administration’s pursuit of war, the decline of trains and the destruction of the environment.

MOYNIHAN STATION HAS all the ingredients for Ms. Moynihan to take on as a crusade. It is a cause where there is a clear right (build it) and wrong (drag it out); where there is an underdog engaged in a long, difficult struggle; where there are great principles at stake; and where there is a chance to avenge a terrible travesty (the destruction of the original Penn Station in the 1960’s).

“Every single meeting I have had with the two Steves, they understand that this is a public works project. They know it is a preservation project,” Ms. Moynihan continued, referring to the chief executives of Related and Vornado, Stephen M. Ross and Steve Roth, respectively. “They have always been extraordinarily open with myself and my mom. We call them up, they hear us out, they’ve shown us everything from the beginning.”

Ms. Moynihan has tried to maintain links to the advocacy organizations that are in some ways her oldest and most natural allies, but it is clear that some distance separates them now. According to its president, Peg Breen, the Landmarks Conservancy helped the Friends of Moynihan Station set up its kickoff party in 2005: a cocktail hour at Farley Post Office with Senators Charles Schumer and Hillary Clinton.

But then, the developers changed their plan. Not only did they want to convert Farley into a roomier, grander entrance to Penn Station’s train tracks, they planned to move Madison Square Garden to the western half of the building, leaving the arena’s current location free for a new Penn Station. But moving the arena could also endanger some of the architectural trademarks in the old post office, which, like the old Penn Station, was also designed by McKim, Mead & White.

Ms. Moynihan was one of the key people whom the developers approached with the idea. While the new plan would make the project immensely more complicated—and take more time and money to complete—she embraced it fairly quickly. In fact, she even narrated a short film that the architect James Sanders wrote and the developers funded and showed to different government figures and civic organizations in order to promote the idea of the two-station solution.

“Maura has been a passionate pragmatist when it comes to this project,” Vishaan Chakrabarti, the president of Moynihan Station Venture, the partnership set up by Vornado and Related, told The Observer in a telephone interview. “She’s got a wonderful, fiery personality and she wants to hear jackhammers. She wants to see this project built. And I think it is refreshing that she saw early on the involvement of the private sector as a positive thing, in that they would add resources and energy.”

At the same time, Ms. Moynihan has tried not to alienate the preservationists, avoiding specific positions on issues such as signage while pushing a general spirit of compromise.

On her purple blazer last Friday, she wore a button that read, “Build it well. Build it now,” which is the slogan of the public awareness campaign that the Friends of Moynihan Station will launch this week. She keeps inviting the Municipal Art Society and the Landmarks Conservancy to meetings of the Friends group—which is run under the auspices of another civic group, the Regional Plan Association—and the three have discussed some sort of position they could all share.

“We’re a civic group very interested in the quality of architecture and planning and we are coming at it from a different perspective than that of a family,” said Kent Barwick, the president of the Municipal Art Society. “I think she wouldn’t pretend to be an expert on either architecture and preservation. Where she has been coming from, and it is useful, is to try to push the project forward.”

The expanded Moynihan station is hardly recognizable as the project that its namesake senator advocated in his final years. It is even questionable—although nobody has bothered to question it—whether it’s worth the public putting in $550 million to renovate Farley since it will only accommodate a third of the riders who will go through the entire complex. The Penn Station overhaul is expected to cost another $2 billion, and, so far, the developers have offered to cover $450 million of that.

According to a source familiar with the plan, once the arena is moved (anticipated to occur in 2011), the current Penn Station would be unearthed and covered with a glass roof, which would let sunlight reach the ground floor and concourses. The state will choose between two plans: One would put large 90-story towers on the north and south sides of the block; the other would put a million-square-foot shopping center there and disperse the remaining development rights to nearby parcels. The state and developers have taken to calling the redone Penn Station “Moynihan East” and the converted Farley building “Moynihan West,” although it is questionable whether Amtrak will change its nomenclature from “Penn Station.”

The plan, while lacking any architectural renderings, has drawn lukewarm reactions from preservationists.

“I think it would be fantastic to do two train stations, and I think moving Madison Square Garden can be done, but it is up to the state to make sure the public does win,” said Ms. Breen. “You don’t want Moynihan East to become a shopping mall and Moynihan West to become a lobby to Madison Square Garden, which I think is what it is becoming.”

Ms. Moynihan knows she has a special status, because of her pedigree, in the fight over the train station, and she tries to keep a statesmanlike distance from the nitty-gritty details as a result. And while this chapter in her varied life, like many others, has put her in the spotlight, she acts as if the station campaign is a chore, or at least a duty, rather than a pleasure.

“When you are living your life, it is very banal,” she said. “It’s full of struggle, pain and confusion and fear. It doesn’t seem at all glamorous, one’s life, when one is in it.”

She wants to see construction started before she returns to Asia. How long she will wait for that, she will not say.