It's the second flight of the $1 billion Spacelab and a shakedown cruise for the first monkeys to travel in space with humans, but the seven-member crew making the 17th flight of the space shuttle Monday call it a flight by scientists for science.

"This mission marks the first time that scientists who designed their own experiments will be executing those experiments in space," said Don Lind, a scientist-astronaut who's been waiting 16 years for this flight. "I think that's a milestone . . . . "

Lind is a physicist. The crew's other scientists are physicians Norman E. Thagard and William E. Thornton; Lodewijk van den Berg, a chemist; and Taylor G. Wang, a physicist. Only Marine Col. Robert F. Overmyer and Frederick D. Gregory are astronaut-pilots. Overmyer will command the flight and Gregory, a black astronaut raised in Anacostia, will be his pilot.

This is to be the oldest crew ever to have flown in space. Lind is 54, van den Berg is 53 and Thornton is 55. Overmyer is 49, Gregory and Wang are 44 and Thagard is 41.

Challenger is scheduled to lift off from the Kennedy Space Center at noon Monday, just 17 days after its sister ship Discovery roared away from that launch pad and 10 days after Discovery landed at Kennedy. It's the fastest "turnaround" the space agency has achieved since the shuttle flights began four years ago.

The countdown was moving smoothly yesterday but the failure of a nine-volt battery like those used in transistor radios forced NASA to cancel deployment of two small satellites carried aboard Challenger. The satellites will be carried into space and returned to Earth rather than be removed from the shuttle so near liftoff. Both are "low-priority" satellites that are almost hitchhikers on this flight.

With the European-built Spacelab aboard the shuttle, Challenger's crew will get to work immediately in shifts around the clock to expedite their 15 experiments. The weightlessness of space is so crucial to these experiments that the crew members have been told to limit in-flight exercise so their movements don't rock the boat in orbit. The five scientists tending the experiments inside the 20-foot-long Spacelab have been ordered to pull their hands back from the experiment racks if they feel a sneeze or a cough coming on.

"The autopilot will fly Challenger the entire time we're in orbit because it's impossible for a man to fly it as tightly as we want it," Commander Overmyer said. "The only time I'll put my hands on the controls will be at 40,000 feet when we're coming in for landing."

The most critical experiments have been clustered near Challenger's center of gravity, the most stable part of the spaceliner. One of these experiments is a "Star Wars" attempt to grow pure crystals of tryglycine sulfate, an infrared detector so sensitive to heat that scientists have predicted that it will pick up from orbit the engine exhaust of a missile seconds after it leaves its silo.

In orbit with the seven-man crew will be two dozen rats and two squirrel monkeys, the first time lower primates will have flown in space with humans. Four rats have surgical implants in their hearts to record changes in heart beat and blood flow in weightlessness.

The squirrel monkeys are on a shakedown cruise to see how they tolerate living in orbit. If they don't get nervous or frightened in space, later flights will carry squirrel monkeys with surgical implants to test for everything from space sickness to heart changes.

"Squirrel monkeys are a good analog for man," mission scientist George Fichtel explained. "They have an upright posture and the same circadian rhythym biological clock as man does."

One of the most intriguing experiments on Spacelab will be observations of the Aurora Australialis, the "Southern lights" that flicker rapidly in the skies near the South Pole at this time of year. Spacelab also carries a French-built widefield camera that is to make its second survey of hot stars whose strong emissions of ultraviolet light can be seen only in space.

Spacelab's mission is scheduled to end at 12:06 p.m. on May 6, after a week-long flight. The flight had been set to land in Florida but was switched to the desert runway at Edwards Air Force base in California for safety's sake after Discovery blew a tire and left shredded rubber on all four landing wheels at Cape Canaveral 10 days ago.

Shuttle managers want to be sure of what caused Discovery's rough landing before committing to another shuttle landing at the Kennedy Space Center.