State investigators spent yesterday crawling over the stalled tram, which lost power Tuesday, stranding many of its 68 passengers hundreds of feet in the air for nearly 11 hours.

Yet no one could say what had caused the power outage that crippled the tram or when it would be back in service.

"We are running a thorough investigation that is looking at all aspects of the operation," said Rob Lillpopp, spokesman for the state Labor Department, which is overseeing the probe.

"The bottom line is that the tram is still closed," he said, "and it will only reopen when we are convinced the people of New York are riding it under safe conditions."

Though a typical investigation usually lasts close to two weeks, the tram could reopen before the review is complete if officials are satisfied the gondolas can operate safely and reliably, said sources close to the probe.

Investigators grew more certain yesterday that a surge of electricity was to blame for shorting out three of the tram's giant fuses.

But Con Edison officials rejected claims by the tram operators that the utility giant was to blame for the power surge.

A series of miscues and foulups - including the absence of a working backup generator - delayed the rescue operation and prevented the NYPD and FDNY from rescuing the last of the trapped passengers until 4a.m. Wednesday.

Catherine Johnson, vice president of operations for the Roosevelt Island Operating Corp. which runs the tram, said her agency would be conducting its own review of the tram system.

The City Council, meanwhile, will hold a hearing Thursday and plans to call Johnson, among others, to testify.

"There needs to be a more widespread understanding of how it is operated and what circumstances led to the breakdown," said Councilman John Liu (D-Flushing), chairman of the Transportation Committee.

Gov. Pataki refused to comment on the tram's future, declining to weigh in until the state review was complete. But other local leaders argued the tram should not be eliminated.

"As soon as the crisis was concluded, there was no fear among riders," said Councilwoman Jessica Lappin (D-Manhattan), whose district includes Roosevelt Island.

"It was simply, 'When can we ride the tram again?'"

With Lisa L. Colangelo