While it was out of touch with Earth Tuesday and Wednesday, the spacecraft Magellan had a kind of panic attack in its orbit around Venus, whirling to and fro, firing its thruster jets repeatedly, possibly trying to respond to conflicting signals from an out-of-control robot brain, scientists said yesterday.

Magellan's weary ground control team has maintained a steady radio link with the craft since late Wednesday, and it has sent them information about its strange behavior while out of their supervision.

But the team said it still does not know what caused the highly automated craft to lose contact with Earth twice in the last week. They assume the complicated spacecraft will go incommunicado again and are developing defensive measures for the spacecraft -- and themselves.

"We'll all be issued pacemakers," joked John Slonski, spacecraft system engineer, referring to the toll the problems are taking on the ground technicians at the Jet Propulsion Laboratory in Pasadena, which manages the mission for the National Aeronautics and Space Administration.

Investigators are examining many possible causes for the problems hampering Magellan's $744 million mission. These include electrical or magnetic activity around Venus, disturbances on the far side of the sun, which is the side facing Venus, a software bug, and even the remote possibility that Magellan's solid-fuel rocket motor failed to fall off after it fired to slow the spacecraft enough to go into orbit around Venus Aug. 10.

At about seven seconds after the separation, engineers noticed "an incident inside the computer," Anthony J. Spear, Magellan project manager, said. "We saw invalid commands being generated inside the {attitude control} computer."

Days later, he said, "What we know is the computer ran amok."

He said Magellan will not start its mission to map the surface of Earth's sister planet, scheduled to begin Sept. 1, until the problem is understood.

But he added, "I'm betting my life. . . that we're going to be turning that spigot on very soon and you're going to love it."

The mysterious problem has caused the craft to lose contact twice in the last week, once for 14 hours and then for 17 hours.

The engineers have programmed the spacecraft with various protections and have drawn up a complex list of commands to send the instant it loses contact again, to start it sweeping the skies immediately in a cone-shaped pattern to recontact its handlers. "The bottom line is, if the spacecraft stops communicating we want to kickstart this coning action," Spear said.

Data show the craft's batteries are fully charged, indicating it kept its solar arrays pointed toward the sun, as it was designed to do. And it had used 5.5 pounds of fuel, about 2 percent of its total, indicating it had trouble maintaining its attitude and seemed to have been going back and forth in a pendulum-like motion at a high rate, he said.