Astronauts Jack R. Lousma and C. Gordon Fullerton suffered a setback on their second day in space today when they were unable to conduct a critical test using the robot arm that serves as the mechanical muscle of the space shuttle Columbia.

Lousma and Fullerton could not complete an important grappling test because the television eye for the wrist portion of their 50-foot-long mechanical arm blacked out each time they tried to turn it on to help latch onto an 82-pound instrument and lift it from Columbia's cargo bay.

On three consecutive attempts, a circuit breaker regulating power to the robot arm's wrist camera interrupted electricity to the camera. On the third try, engineers at the Mission Control Center here saw 11 amperes of power surge through instruments monitoring the arm, almost surely signifying that the robot arm was being short-circuited and rendered useless.

"When I went to do the grapple test, I got no picture and I looked down and noticed the circuit breaker had popped out," Lousma said after the third attempt to latch the wrist onto the instrument. "That's a bad one to lose."

Loss of the wrist camera means the astronauts cannot use the robot arm as planned on the seven-day flight. Mission directors canceled one test of the arm tonight and postponed any attempt to use the wrist in the grappling exercise considered the most important test planned for the arm in the next five days.

The key test of the wrist was to involve grappling and latching onto an instrument called the Plasma Diagnostics Package, an 82-pound combination of instruments that the arm was to move as far as 50 feet from the shuttle to measure the electromagnetic wake Columbia leaves as it moves through the earth's ionosphere at an altitude of 150 miles.

The wrist camera is crucial any time the arm is used to grasp an instrument or a satellite and remove it from the cargo bay--one of the shuttle's main purposes during its 12-year operational period.

At the end of the 50-foot arm, the wrist is too far from the astronaut operating the arm from the shuttle's cabin for him to see what he is doing without help from the camera.

Flight directors were to decide early Wednesday whether to reschedule the test. One alternative involved having Fullerton use a camera at the arm's elbow to maneuver the arm as close to the instrument as possible, then use binoculars to lock the arm onto the instrument.

Loss of the wrist camera also meant the astronauts could not get a close look at the shuttle's nose, which suffered damage to its heat protective tiles during Monday's launch from Cape Canaveral, Fla.

Moving the arm above their cockpit today, Lousma and Fullerton used a second camera strapped to the arm's elbow to study liftoff damage. As many as 25 of the white tiles covering the spacecraft's nose were stripped away by aerodynamic forces at liftoff or ripped loose when ice on the fuel tank broke loose and battered the nose after liftoff.

When the arm was turned and focused at the tail, the elbow camera saw that as many as 12 of the black tiles near the tail also were missing, presumably because of the same forces that ripped off the nose tiles.

The missing nose tiles cover a surface subjected to temperatures of between 400 and 800 degrees Fahrenheit during reentry into the atmosphere. Tiles near the rear reach temperatures of 1,200 to 1,500 degrees Fahrenheit but faced the greatest heat during ascent.

"We feel we're safe," Deputy Shuttle Program Manager Thomas Moser said. "We are looking at some contingency plans for reentry, but we do not anticipate any problems on entry and landing next Monday."

The astronauts today recalled seeing pieces of white material, possibly tiles or pieces of tile, falling on their windshield during liftoff. Lousma today had to take Scopdex, a mixture of scopolamine and Dexedrine, to fight nausea and motion sickness. He suffered the same ailment when he flew on Skylab in 1972.

Lousma had slept fitfully Monday night because it was his turn to sleep sitting up in the cockpit with his headset on. "Every time I got near the northern latitudes," he complained, "I kept getting a little noise in my ear . . . every time we hit the most northerly point in the orbit."

Johnson Space Center engineers speculated privately that the static came from over-the-horizon radar operated by the Soviet Union near the Black Sea.