With time running out, the space shuttle Discovery finally thundered into orbit tonight and set off after the crippled Hubble Space Telescope for a down-to-the-wire orbital overhaul.

Already running two months behind schedule because of a series of technical problems and bad weather, Discovery rocketed away as scheduled at 7:50 p.m., lighting up the cloudless night sky for miles.

Eight-and-a-half minutes later, Cmdr. Curtis Brown and his six crewmates slipped into their planned preliminary orbit, one that will set up a Tuesday rendezvous with the Hubble Space Telescope.

"I'm thrilled to pieces," said Hubble project scientist David Leckrone. "I had convinced myself we weren't going to go after the washouts the last couple of nights, so this is a very nice Christmas present indeed."

The first of three back-to-back repair spacewalks is scheduled to begin Wednesday afternoon. If all goes well, Discovery's crew will release the refurbished telescope back into open space around 6 p.m. Christmas Day.

The millennium's final manned space flight is scheduled to touch down here on Dec. 27. That will give ground crews time to drain toxic propellants and power down the orbiter before the end of the year.

Concern about possible Y2K computer problems after touchdown prompted NASA to set this weekend as the deadline for getting Discovery off this year. Another delay would have forced NASA to reschedule the launch for Jan. 13.

As it is, the astronauts will not be able to carry out a full-duration mission. To get back to Earth by Dec. 27, the crew will have to eliminate a planned day off in space and, more important, one of four planned Hubble repair spacewalks.

But tasks planned for the fourth spacewalk were more preventive maintenance than requirements and their loss will not affect the operation of the telescope.

The fourth spacewalk "activities were very low priority relative to everything else we're doing," Leckrone said.

NASA originally intended to launch the next Hubble servicing mission in April. But last February, the third of six stabilizing gyroscopes aboard the telescope failed, leaving the $1.5 billion satellite just one failure away from scientific shutdown.

NASA managers then decided to break Servicing Mission 3 into two parts and to launch a quick-response repair mission, known as Servicing Mission 3A, on Oct. 14 to replace all six gyroscopes as quickly as possible. But wiring problems discovered in the wake of a July shuttle flight forced NASA to repeatedly delay Discovery's flight.

In the meantime, a fourth gyroscope failed aboard Hubble on Nov. 13, leaving the telescope with just two operational gyros, one less than the bare minimum needed to keep the telescope locked onto astronomical targets.

The telescope has been in electronic hibernation, awaiting the arrival of Discovery's crew.

"I feel better about it now," spacewalker Michael Foale said during a pre-launch countdown rehearsal. "Because now we really are going to put the telescope right, get it back into service producing science."

Joining Foale and Brown for the 96th shuttle mission are pilot Scott Kelly, Frenchman Jean-Francois Clervoy, Steven Smith, John Grunsfeld, Foale and Swiss flier Claude Nicollier.

Along with replacing Hubble's malfunctioning gyroscopes, the astronauts plan to install an upgraded flight computer, a new S-band radio transmitter, a refurbished guidance sensor and a solid-state data recorder to replace an aging reel-to-reel model.

They also plan to install a new radio transmitter and voltage regulators that will prevent Hubble's six batteries from overheating.

During Servicing Mission 3B in 2001, astronauts are to install two new solar arrays, a new camera and a high-tech refrigerator designed to restore a dormant infrared camera to operation.

In addition, wallpaper-like insulation will be installed to keep Hubble from getting too hot or too cold, work originally planned for the current mission.

"We fly in space to make people's lives better, and the Hubble Space Telescope has gathered lots and lots of information to help us understand where we came from, and potentially, where we're headed," lead spacewalker Smith said in a NASA interview. "So to be part of that is incredibly rewarding."

CAPTION: In a time-exposed shot, the shuttle streaks into orbit above lighted boats on the Indian River in Florida.