Additional delays could disrupt the convention center construction schedule so that the facility's main exhibit halls would open before the shed, designed as the entrance, is complete.
City and authority officials said privately, a drawn-out fight over the cleanup could lead to a decision to redesign the $500 million-plus convention center without the shed.
"The city's position is that there's additional work that has to be done and that it's Reading's responsibility to do it," said James J. Cuorato, assistant city commerce director.
Harry M. Perks, executive director of the convention center authority, said that engineers representing the authority briefed consultants from Reading yesterday on studies showing that low, but unsatisfactory, levels of asbestos and PCBs remain in the shed.
Perks said that Reading Co. officials "haven't said they would or would not" agree to finish the work.
Officials from the Reading Co., which owns the shed and the popular market below it, were unavailable yesterday for comment.
Reading officials said last month that they were standing by the findings of their own environmental consultants, who said in a report filed with the city in mid-February that the cleanup was complete.
"We've completed our obligation in accordance with the agreement (with the city), and we've had a professional engineering firm certify that we have," was the statement issued March 12 by James A. Wunderle, Reading's executive vice president.
According to Perks, consultants for the city and the authority found that the level of contamination at the shed was low but not low enough to meet federal environmental standards.
He estimated that it should take about a month to complete the cleanup. The city and the authority then would need more time to re-examine Reading's work.
His "optimistic" projection, Perks said, was that the process could be completed in six weeks.
Perks played down the gravity of the latest dispute, saying he believes the two sides will work amicably together to clean the remaining contaminants from the shed.
"The bottom line is that Reading wants to sell the shed and we want to buy it," he said.
The long-running dispute between the Reading Co. on one side and the city and convention center authority on the other dates to September 1988, when Reading was to have finished removing asbestos and PCBs from the train shed.
Clearing the hazardous chemicals was Reading's responsibility under a 1987 sale agreement in which the city agreed to buy the shed, the market and surrounding Reading properties needed for the convention center and an adjoining hotel.
Plans call for the convention center to be built above and adjacent to the market in an area bounded by 11th, 13th, Race and Arch Streets.
Under the agreement, the city was to buy the Reading properties no later than 30 days after Reading certified that the environmental cleanup was finished, subject to a review by consultants for the city and the authority. Reading filed that certification in mid-February.
Officials for the city and the authority have been reluctant to discuss the long-term effects of the dispute. Some have conceded privately that unless the authority can gain access to the shed within the next few months, it may have to be eliminated from the project.
Doing so would be a major blow to city officials and other supporters of the convention center, who have pinned their hopes on the shed as the single feature that will distinguish Philadelphia's convention center from other convention facilities in the United States.
Perks maintained that removing the shed would not be considered unless the authority could not gain access to it "six months down the road."