Governor Spitzer’s steamroller may run into a wall at ground zero when it comes to the Port Authority’s planned PATH Station, for which cost estimates are skyrocketing and a redesign is under way. The soaring, skeletal transportation hub was designed by Spanish architect Santiago Calatrava to invoke a flying dove and to act as the Grand Central Terminal of Lower Manhattan. It could face significant modifications in coming months, according to several sources familiar with the plans.

Mr. Calatrava, an internationally renowned architect and engineer who recently had an exhibition at the Metropolitan Museum of Art, is said to be resisting changes to the project’s “design integrity,” according to sources familiar with the plans. Mr. Calatrava could not be reached for comment yesterday. The new PATH station is budgeted at $2.2 billion, but sources say recent cost estimates could drive up the price tag by about $1 billion. The Federal Transit Administration has committed to cover $1.9 billion of the cost, part of a $4.55 billion federal transportation package delivered after the terrorist attacks of September 11, 2001. The Port Authority, a bi-state agency governed by officials from New York and New Jersey, is committed to pay $300 million.

A Port Authority official said a company contracted by the agency to negotiate deals with contractors recently produced cost estimates that exceed the budget. The official said the Port Authority feels the estimates are inflated, but said the agency would be willing to make changes to the design as long as the basic concept of the project stays the same. One of the changes being considered would replace the steel with less expensive concrete.

Another development official likened the PATH terminal situation to the design modifications and “value engineering” that took place for the World Trade Center Memorial project last spring, when revised estimates said the memorial would cost about $1 billion. After cost-cutting and design changes, it is now on course to be built for about half that amount. The elaborately designed PATH station would replace the terminal that was destroyed more than five years ago when the twin towers came down. Before the attacks, there were 67,000 daily boardings at the station, according to the Port Authority. Roughly 1 million people a day pass through Midtown’s Grand Central.

The new PATH station is not an easy structure to build, according to sources familiar with the plans. The structure is to contain a grand hall, retail stores, and connections to the area’s other transportation networks. Its roof is designed to open to the sky once a year to commemorate the terrorist attacks. Critics of the project say it amounts to an extraordinarily expensive public art project, and will not increase the system’s transit capacity.

Following the redevelopment agreement struck in April, the Port Authority must prepare the eastern side of the 16-acre site, which includes the PATH station, on a tight schedule to clear the way for developer Larry Silverstein’s three office towers. If the Port Authority does not turn over the office sites to Silverstein Properties by its deadlines, it must start paying Mr. Silverstein $300,000 a day in summer 2008. According to plans, the Port Authority must build another entrance to the existing PATH station on the north side of the former World Trade Center site and raze the existing temporary station, which was built for $323 million and opened in November 2003. The Port Authority would then need to excavate the site, and eventually build out the new station. It is scheduled to be completed at the end of 2009.

Construction cost increases are a growing problem in New York City, and are now estimated at between 1% and 2% a month. The cost of the MTA’s Fulton Street Transit Center, just a couple of blocks from the planned PATH station, has now risen to $888 million, from about $740 million, and the scope of the project has been repeatedly scaled back.

A spokesman for the Regional Plan Association, Jeremy Soffin, said cost increases at the new PATH station would not be surprising in the current building environment.

“Escalating costs are an issue with construction on all kinds of projects around the region. You will be seeing more and more reports in the coming months about projects that are over budget due to the high cost of construction,” Mr. Soffin said.

He said he doubted that the design would be stripped from the station during a reconfiguration of plans. “It’s a key piece of the rebuilding effort downtown. It is an important transportation project, but it will also serve as an important public space,” Mr. Soffin said. Ultimately, the Spitzer administration could be responsible for dealing with the increased costs. Mr. Spitzer’s leading downstate development official, Patrick Foye, has yet to be officially elected to the board of the Port Authority, although he is expected to be soon. Mr. Foye’s office would not comment yesterday. Mr. Spitzer’s spokeswoman did not respond to phone messages.

One source familiar with the redevelopment plans said the new team in Albany is trying get a clearer, “more honest” financial picture of the redevelopment at the former World Trade Center site in the wake of the Pataki administration. A spokesman for the Port Authority, John McCarthy, said the PATH station is on budget. “The project is on schedule and the design is unchanged,” he said. “While escalations are a potential for any long term project for a market with increasing costs, any increase would require board approval.”

Robert Gottheim, an aide to Rep. Jerrold Nadler, a Democrat whose district includes ground zero, said: “We need to really investigate into why the costs have skyrocketed so much. We have to make sure we are spending he money correctly, and the costs are in line with the benefits.”