The space shuttle Discovery passed the halfway point of its maiden voyage today as the second American woman in space raised an experimental solar panel more than 10 stories above the ship's cargo bay.

Taking no more than four minutes each time, astronaut Judith A. Resnik twice fully unfurled a 102-foot-tall lightweight solar mast into space as the nation's newest spacecraft circled Earth at 17,500 miles an hour.

Resnik partially extended and retracted the panel repeatedly at different speeds as Discovery commander Henry W. Hartsfield Jr. and pilot Michael L. Coats pitched, rolled and yawed the shuttle to see how the experimental panel would withstand routine maneuvers in space.

"The test went very well," said flight director Randy Stone at the Johnson Space Center in Houston.

"The tests went beautiful," rejoined Gary Turner, solar wing program manager for the Lockheed Corp., which built the $7.6 million lightweight panel for the National Aeronautics and Space Administration. "We did twice the number of tests we scheduled today and did half of tomorrow's work today. There were no surprises, nothing that concerns us about how these solar panels will work in space on future missions."

A problem arose later, however, when an ice buildup blocked lines that dump waste water overboard from the shuttle, causing Mission Control to order the crew not to use the craft's toilet. The crew planned to resort to Apollo-era plastic bags carried by the shuttle for emergencies.

Flight director John Cox said the crew might attempt on Monday to knock the jagged 18-inch chunks from Discovery's flanks with the vessel's robot arm. Further solar panel tests were postponed until the problem is remedied.

Cox said the cause of the freeze was unknown. "We don't have a theory," he said. "For all we know this may have been occurring on previous flights."

Apart from the discomfort of having no toilet, the astronauts were in no danger. The only major concern was that the ice might break off and damage the craft's heat-dissipating tiles during reentry Wednesday.

The ship was turned toward the sun to help get rid of the ice, but Cox said it might not melt as fast as hoped.

Also, he said, the solar panel could not be extended again if the ship were kept with its port, or left side, facing the sun. Among the possibilities being considered were using the shuttle arm to knock off the ice, or jarring it off by firing the ship's engines.

Today's solar panel experiment moved the shuttle program closer to the day when the auxiliary power the panel provides will enable missions to be extended to as many as 20 days. Past satellites and spacecraft have been equipped with large, rigid solar panels to provide them with electricity. They have been heavy, bulky and expensive, weighing eight times more than the Lockheed panel weighs and costing twice as much for the power output they're designed to produce.

The new, foldable panel is expected to supplant the older solar arrays, which could not be restowed to prolong their life. The Lockheed panel can be routinely redeployed, as Resnik demonstrated.

"We see very little wobbling of the mast as it extends out to 100 feet," Resnik said this afternoon as Discovery made its 53rd orbit of Earth. "The panels are not sticking the way they did the first time, either, and it looks like it's passing all its dynamic tests very, very nicely."

Lockheed's Turner said that engineers on the ground saw a wobble in the solar wing when it was half-extended. Ground experiments had led them to expect such a wobble, he added.

"It wasn't much of a wobble, maybe two- or three-inch side-to-side motion at the halfway point and near the end of its full extension. It's of no concern to us," Turner said.

Successful testing of the experimental solar panel means that a flightworthy version may be used on a shuttle mission before the end of the decade.

Larger versions of the panel that was tested today are expected to provide electricity for the nation's first permanent space station, which is planned to be built and manned in 1992.

Turner said it was gratifying to see the panel perform well in space.

"I stopped worrying as soon as we got that thing in space. You have no idea how hard it is to test that thing on the ground, where it will only support one three-hundredth of its own weight. In space where there is no gravity, it worked just perfectly," he said.