With weather forecasters predicting flash flooding and heavy thunderstorms in New York City, the Metropolitan Transportation Authority faces the possibility of additional service shutdowns Friday as it struggles to clear tracks of debris left from Tuesday’s flood and readies the system to handle more rain.

Buses from Long Island were put on reserve last night to handle city customers whose subway service could be compromised again Friday, and all construction on the system was set to be halted, transit officials said. Extra personnel were preparing to station themselves throughout the system to provide more information to customers, who on Tuesday were left in the dark about which train lines and stations were out of service during a systemwide meltdown.

The preparations came as the subway system was resuming normal service after a rainstorm Tuesday shut down almost every train line and left thousands of New Yorkers sweating through their shirts as they walked to work or pushed their way onto overcrowded buses.

While the MTA last night rushed its 500-pound portable pumps to problem spots in the system, officials said having those pumps in place earlier this week would not have helped to prevent Tuesday’s problems.

“There was only one location where we could have used the pump train,” a senior vice president of subways, Michael Lombardi, said. The MTA has three pump trains, but could not use them Tuesday.

Portable pumps, which the MTA’s inspector general recommended investing in following a major subway flood in 2004, were used only at Hillside Avenue on Parsons Boulevard Tuesday.

Following a directive of Governor Spitzer, the MTA yesterday announced that it is convening a task force of transit and city officials, as well as academics to study how improvements can be made on weather forecasting, communications with customers, engineering issues that left a waterlogged system unusable earlier this week. The task force is also going to study climate change, the executive director of the MTA, Elliot Sander said.

“I don’t want to say the MTA is blaming this on climate change,” Mr. Sander said yesterday at a press conference at MTA headquarters. “Our sense is that there’s a rapidity of storms with a ferocity that we did not encounter until the last several years.”

The commissioner of the city’s Department of Environmental Protection, Emily Lloyd, and the MTA’s inspector general, Barry Kluger, as well as the heads of every MTA subagency, were among those appointed yesterday to serve on the 30-day task force.

Mr. Sander said the MTA would consider adding an extra day to MetroCards to reimburse riders for a missed day of service.

City officials who had been blaming the MTA for the service failures, meanwhile, seemed ready to give the transit authority a chance to redeem itself.

“We have a different MTA and a different governor than we did three years ago,” the City Council speaker, Christine Quinn, said, noting that it was up to the city “to hold the MTA’s feet to the fire.” Mayor Bloomberg said that while “nobody is satisfied with the MTA’s performance,” the bottom line is that the subway system is “usually pretty reliable.”