Today's postponed space walk by shuttle astronauts William Lenoir and Joseph Allen was given the green light for Monday after flight surgeons decided Lenoir was over his spell of motion sickness.

"Bill Lenoir reports he is doing better every hour," flight director Tommy Holloway said this afternoon at the Johnson Space Center, where the flight of the Columbia is directed. "He said he was feeling 100 percent this morning so I assume he's 105 percent by now."

While Lenoir and Allen prepared for their walk, Cmdr. Vance Brand and pilot Robert Overmyer maneuvered the shuttle with a series of five small engine burns onto a new flight path designed to bring the 100-ton spaceliner down at Edwards Air Force Base in California's Mojave Desert at 9:33 a.m. (EST) Tuesday, about four minutes later than originally planned.

"This gives us a little better daylight condition at landing," Holloway said. "What it also does is increase our cross range a little bit, which means we'll have to watch it more closely to make sure we don't have to correct for too much cross range." Cross range means the number of banking turns the astronauts will have to make to line up with the concrete runway at Edwards.

If Lenoir sleeps well tonight and eats his breakfast without trouble, he will step out of Columbia's airlock at 7:50 a.m. EST to take America's first walk in space in almost nine years. Parts of the walk will be televised live.

Minutes after Lenoir hooks his waist tether to a slide wire and moves down the starboard side of the cargo bay, Allen will follow on the port side.

Lenoir will need to be fit. In the 3 1/2 hours he and Allen plan to move up and down Columbia's 65-foot-long cargo bay, held down by pulleys and holding onto handrails and foot restraints, they will perform tasks that involve manipulating more small parts and tools than most astronauts handled outside orbiting spacecraft through the Gemini, Apollo and Skylab programs.

Lenoir's trickiest task will be to simulate the repair of an electronics box identical to the one that has broken down on an orbiting spacecraft called the Solar Maximum Mission. The simulation will be repeated by the astronauts of the 11th space shuttle flight early in 1984 and then done for real late in 1984 when the crew of shuttle flight 13 attempts to repair the electronics box on the now-useless spacecraft.

The toughest part of walking in space is dealing with the heat generated inside the space suit, in part from the body's own strenuous effort to move while weightless, in part from any heat radiated by the suit's electonic gear and in part from the sun beating down on the space walkers.

Lenoir and Allen will test a new suit, one that has better cooling, lighter weight and affords more mobility. Underneath the bulky outer suit, they will wear a cooling garment -- the "spaghetti suit" -- which resembles long underwear lined with 300 feet of plastic tubing through which water chilled to almost freezing is pumped.

Before their walk, Lenoir and Allen will wear the suits for almost three hours, breathing pure oxygen at a pressure of five pounds per square inch instead of the routine mix of nitrogen and oxygen they breathe inside the cabin at the sea-level pressure of 14.5 pounds a square inch. The procedure should wash the nitrogen from their blood and prevent them from getting the bends when they return to the airlock.

Holloway said the shuttle crew has accomplished all of its major objectives, except for the space walk. He said the only piece of complex machinery aboard the shuttle that had broken down was one of four cathode ray tubes that give the crew television images of the spacecraft. It was repaired today by Overmyer, who removed floor panels and switched the cables supplying power to the tube.

There was also one hitch on the ground, when an electrical fire in the Mission Control Center Saturday night short-circuited a cable, blacking out a computer at 9:50 (EST). The computer stayed down for three hours while flight directors switched to a backup.

Flight directors were unable to talk to the astronauts or receive data from Columbia for more than 30 minutes while the spacecraft flew over Dakar and Madrid. The astronauts were asleep at the time, but had they been awakened, they would have been unable to communicate.

Today, the shuttle astronauts spent part of their time ducking down to Columbia's lower deck to tend locker boxes containing three experiments designed and built by Scott Thomas of Utah State University, Aaron Gillette of Western Carolina University and Michelle Issel of American University.

Issel's experiment is an attempt to grow sulphate salt crystals to see if weightlessness does away with the tiny lumps and bumps that form on crystals grown on Earth. Gillette's is an attempt to grow sponges soaked in different chemicals that correspond to the Florida seawater, where sponges grow best in America.

"Aaron has a theory that sponges grow using the force of gravity to help them," Allen said, "and we're testing that by permitting sponges to grow here, if they indeed will grow."

Thomas' experiment will try to find out if fluids flow the same way in space they do on Earth. In his box, Thomas placed four different samples of oil on flat-bed pans warmed by tiny electric heaters. As the oil gets warmer, it should thin out and move along the pan while a camera records its movement.

While it hardly seemed as momentous as the launch of a $50 million communications satellite the other day, the test brought broad smiles to the 18-year-old Thomas as he watched from Mission Control.

"Tell Scott, no bumps and no jiggles," Allen said. "I promised him . . . ." Replied Mission Control: "He has been so informed."