Discovery's astronauts packed Friday for the end of their 1.9 million-mile voyage and prepared the shuttle for a fiery plunge toward a dawn landing Saturday on a California desert.

Discovery commander Michael L. Coats and pilot John E. Blaha planned to run through a series of tests Friday to make sure the shuttle's computers and control jets were ready for the return to Earth.The other astronauts made final runs on a group of experiments and followed a script to shoot the last 4,000 feet of film in a powerful 70mm IMAX camera used principally to study the Earth's environmental trouble spots. Then they were to stow their equipment for the trip home.

All of the crewmen stopped their work for an interview arranged with the "Today" show on NBC, but then found they had to wait more than three minutes while the network completed a feature on Texas dove hunting and ran four commercials.

Asked about environmental damage viewed from space, James F. Buchli said the scale and scope of air pollution "is much more dramatic" seen from orbit.

"What we're trying to do is get some evidence and documentation to bring back and show people just how much we are dumping into the atmosphere and perhaps get a feel how that might affect us in future generations," the astronaut said. "You can see (it) very, very well from here."

Coats said that early in the mission, when an electrical problem forced the astronauts to reduce power usage, "it wasn't really a great deal to us."

"We powered down a lot of our computer displays. We powered down our lighting as much as possible," he said. "It was a little bit of an inconvenience, but not a real impact on our work."

Discovery's early bird crew pre-empted the traditional morning music from Mission Control in Houston for a third day in a row.

A few minutes before they were to be awakened, the astronauts beamed to Earth a tape of "Hi Ho, Hi Ho, It's Off To Work We Go," the work song of the seven dwarfs in the animated movie classic "Snow White."

Mission Control capsule communicator David Low, referring to the seven dwarfs, responded, "We can account for Grumpy, Sleepy, Happy, Sneezy and Doc up there. Who wants to sign up to be Bashful and Dopey."

"I'm not gonna touch that," said Coats with a laugh.

The other Discovery astronauts are James F. Buchli, Robert C. Springer, and Dr. James M. Bagian, a physician.

Early on Saturday, Coats and Blaha will fire two powerful rockets on the back of Discovery to slow the craft and allow it to drop into the Earth's atmosphere. The shuttle will then make a powerless glide halfway around the world and land at 6:36 a.m. PST at Edwards Air Force Base, Calif., in the Mojave Desert.

The landing will complete a flight of four days, 23 hours and 38 minutes that circled the Earth 79 1/2 times.

If the shuttle lands at the time scheduled, the mission will have been about 1 1/2 hours shorter than planned. Discovery was launched almost two hours late on Monday, because of weather considerations, and this put the craft in position to land in California one orbit early.

NASA officials said the forecasts call for good weather at Edwards for the shuttle landing. About 200,000 people are expected at the base.

Discovery will return to Earth with almost three miles of film shot with the IMAX camera. The crew captured views of urban sprawl, of pollution patterns in the oceans, and of vast areas in South America where the tropical rain forest is being cleared and burned.

The camera also photographed floods in Africa, burned areas of the Florida Everglades and western United States, and erupting volcanoes in South America and Southeast Asia.

Film will be edited to create a study of the environmental wounds inflicted on the Earth by industrial man. It is a joint project of NASA and the Smithsonian Institution.