To avoid penalties of $300,000 a day, the Port Authority of New York and New Jersey is racing to finish work on the east side of the former World Trade Center site by the end of the year. Real estate industry experts are skeptical it will be able to meet the January 1 deadline.

Following the redevelopment agreement struck in April 2006, the Port Authority, which owns the property, is in charge of excavating and building slurry walls along the eastern portion of the site to prepare it for the construction of three large office towers being developed by Silverstein Properties. If the Port Authority does not finish the work by the end of the year, it will have to pay $300,000 each day to Silverstein Properties, which leased the World Trade Center site six weeks before it collapsed.

Construction workers for the Port Authority are now working 10-hour shifts to prepare the site, with two shifts of workers Monday through Saturday. Some additional work also is taking place on Sundays, but not at the same level as the rest of the week, a spokesman for the Port Authority, Steven Coleman, said

The president of the Real Estate Board of New York, Steven Spinola, said the Port Authority is working “extremely hard.”

“There is a shot they will make the deadline,” he said in a recent interview.

Another downtown development official said it is “unlikely” the Port Authority, a bi-state agency controlled by appointees of the governors of New York and New Jersey, would prepare the site before deadline.

Mr. Coleman wrote in an e-mail message that the Port Authority’s “plan remains to deliver the site on December 31.”

The developer, Larry Silverstein, yesterday announced that his company had hired the Yonkers Contracting Company to build the foundations for the two office towers, a move that could put more pressure on the Port Authority. In a news release, Silverstein Properties said it expects to begin work on January 2, and a spokesman for the company said the company had received no indication that the work would be delayed.

The first of the two office buildings to be built along Church Street, known as Tower 2, is designed by architect Fumihiko Maki, and the city has a tentative deal to lease 600,000 square feet of office space from the developer. The second tower to be built, known as Tower 3, is designed by Lord Richard Rogers and is slated to rise about 1,050 feet and contain about 2 million square feet of office space. Both are scheduled for completion in 2011.

The World Trade Center project director for the Silverstein Properties, Janno Lieber, said in a statement that the company would keep to a tight schedule as it begins construction.

“As we have seen from the market, New York’s economy urgently needs new first-class office space in order to retain jobs and maintain a competitive edge in the global economy,” he said.