City officials say they waited hours to begin rescuing 68 people stranded midair on both Roosevelt Island trams Tuesday evening because their goal was to get the power back on, rather than stage a risky and untried rescue operation.

The 30-year-old tram system has failed off and on over the years, most recently last September. Tuesday night was the first time engineers were unable to bring power back within a few hours.

Police and fire officials gave up hope of restoring power after about three hours and resorted to a backup plan that relied on a slow-moving rescue basket that had never been used before. The rescue operation did not begin until nearly 11 p.m., after police conducted a test run with no passenger on board. The entire process, which was broadcast on live television until after midnight, took until about 4 a.m.

“Our emergency response people did exactly what they were supposed to do,” Mayor Bloomberg said when reporters asked why the rescue operation took so long. “This is not a race so that you can beat a deadline for your television interview.”

The trams stalled just after 5 p.m. Police emergency service officers began the rescue operation, which included consultations with the tram’s manufacturer in Switzerland, at around 8:30 p.m.

The Roosevelt Island Operating Corporation, a state-controlled entity that runs the tram and maintains the small island of 10,000 people situated between Manhattan and Queens, blamed the tram failure on a power surge that knocked out three of the tram’s four electrical supplies.

The trams’ electrical system is decades old and only a handful of engineers know how to keep it running, or how to bring it back online after a power failure. In this case, even those engineers failed to fix the problem. Con Edison officials said yesterday that they were not responsible for the power failure.

Rescuers had to rely on a weak power current that provided a small amount of energy to operate the rescue basket used to retrieve 47 island-bound passengers. The basket moved slowly along the trams’ suspension cables, and as the process dragged on police brought in a crane to remove passengers in the Manhattan-bound car, who were hanging in a gondola above the East Side.

That slow, tedious operation brought everyone to the ground without injury, but raised questions about the Roosevelt Island Operating Corporation’s oversight of the tram system.

“Last night’s dramatic events highlight the dearth of emergency preparedness by the Roosevelt Island Operating Corporation,” Assemblyman Peter Grannis said in statement. “The fact that this happened was bad enough, but the failure of the backup power supply and the manual retrieval system is inexcusable and the Pataki administration should be held accountable.”

Rep. Carolyn Maloney and Council Member Jessica Lappin, who also represent the island, said the operating corporation has long been underfunded.

“The governor has insisted that the island be self-sufficient and has refused to fund it,” Ms. Lappin said. “This may be the chickens coming home to roost.”

“Roosevelt Island is a self-sufficient authority, raising and managing their own revenue,” a spokeswoman for the governor, Lynn Krogh, said. “Yesterday’s event was a mechanical issue, not a financial one.”

The president of the RIOC, Herbert Berman, said at news conference yesterday that he did not yet have answers about why the trams were brought to a halt. Messrs. Bloomberg and Pataki said investigations were under way and that tram service would not resume until the problem was understood and fully fixed.

In September, the one engineer who knew how to get the power going, Armando Cordova, was stuck in a traffic jam in Westchester and was picked up by helicopter. He was on the scene Tuesday night.

According to officials with the operating cooperation, the tram system has a $3.1 million operating budget. The corporation also just approved a $4 million overhaul to upgrade the system, sources said.

Meanwhile, emergency responders, who have fought turf wars during past crises when determining the lead agency on the scene, touted their ability to work side by side. The operation was handled as a so-called unified command, meaning that the Office of Emergency Management coordinated the fire and police officials.

The RIOC has had its share of problems over the years. In 2003, Robert Ryan was fired as its head in part for awarding himself a handsome bonus for his work in Lower Manhattan after the attack of September 11, 2001.

Assemblyman Richard Brodsky, who released a report on the ROIC, said yesterday that Mr. Berman has been much more responsive, but that there are still improvements to be made.

“This was a state authority,” Mr. Brodsky said. “It was a patronage dumping ground. For a variety of reason I think there’s been improvement.”

“We still don’t know what happened here,” he said. “Everybody deserves an opportunity to explain themselves, but this falls squarely on the shoulders of RIOC.”

The Roosevelt Island tram is similar to gondolas at ski resorts around the world. That could change if planners for Governors Island go through with efforts to create a tram system serving that island, Manhattan, and Brooklyn.

“Technology has advanced a tremendous amount over the last three decades, and we are confident that anything built with those advances would operate with little or no problem,” a spokeswoman for the Governors Island Preservation & Education Corporation, Yvette DeBow, said.