A National Aeronautics and Space Administration spokesman said a new launch could be scheduled for late next week. A planned liftoff on Wednesday was called off because of a faulty fuel gauge that could have prevented Discovery from reaching orbit safely.

NASA must get the shuttle into orbit by July 31 or be forced to wait until September 9 for a new launch window for Discovery and its seven crew.

"It is clear we are still looking at launching during this window," said NASA spokesman Allard Beutel.

After giving up hopes of sending the shuttle into orbit on Sunday, US Discovery program managers at the Kennedy Space Center were to meet Friday afternoon to decide their next move.

Hundreds of engineers were mobilized to study as many as 200 potential causes for the malfunctioning fuel gauge system, and what needed to be done to fix it.

If the shuttle is not ready in time for a July launch, NASA will have to wait for the next launch window, which runs from September 9 to 24.

The delay is a major disappointment for the agency, which has sought to re-establish the prestige of the US space program after Columbia burst into flames and broke up as it re-entered Earth's atmosphere on February 1, 2003.

All seven crew members were killed, and NASA grounded the remaining shuttles in its fleet.

The agency was forced to completely rethink the shuttle program and has made major changes to the shuttles to reduce the risk of a new accident.

The new delays were compounded by NASA's desire to launch during daylight hours. This leaves only a limited timeframe during which Discovery can lift off for its rendezvous with the orbiting International Space Station.

NASA officials did not sound very optimistic.

Wayne Hale, deputy shuttle program manager, described the problem with one of four fuel sensors as an "intermittent failure," which he said was "the worst kind of thing to troobleshoot."

"We're in the early stages of the troubleshooting," he said Thursday.

If the problem is serious, NASA will have to roll the shuttle back five kilometers (three miles) from its seashore pad to its hangar.

The faulty sensor is one of four that sends data on the levels of hydrogen in the spacecraft's massive external fuel tank, to determine when the three engines should be shut off during the ascent into orbit.

NASA experienced a similar problem in April but never established what caused it. The problem disappeared at the time after technicians replaced the cabling and the electronic boxes attached to the gauges.

NASA's plans were also disrupted Tuesday when a plastic and foam protective cover fell 20 meters (60 feet) off one of Discovery's windows, damaging tiles on one of the two orbital maneuvering systems.

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