The two astronauts who last week flew the space shuttle into orbit and home to Earth described the winged Columbia yesterday as an incomparable flying machine that will give the United States "routine access" to space for the next 20 years.

"This flight gives us what we've been trying to do the last 10 years -- it gives us routine access to space," Columbia commander John W. Young told a press conference at the Johnson Space Center in Houston. "I tell you, we're going to get this thing operational sooner than anybody thinks."

So flawless was Columbia's maiden flight that it may make its second test flight as early as Sept. 23, a third flight as soon as Dec. 31 and its final test flight on April 30, 1982. If the National Aeronautics and Space Administration adheres to that kind of schedule, Columbia could "go operational" and carry commercial satellites into space as early as Sept. 15, 1982.

The way Young and astronaut Robert L. Crippen talked about Columbia yesterday, it sounded as if it could go operational next month. Young said they had 135 flight objectives and completed 135.

"I think we got 'em all," said Young. "It was a mission that can truly be called what NASA calls nominal, although I think you're going to have to call it phenomenal. We're going to do away with that word, 'nominal."

"Nothing failed," said Crippen. "Statistically, I didn't think that was possible. We've been working three years to learn how to handle catastrophes and all we did the whole time was sit back and enjoy it."

From the time they left Cape Canaveral, Fla., until they touched down at Edwards Air Force Base, Calif., Young and Crippen said that Columbia responded to everything they asked.

They went into orbit with 13,000 pounds of fuel in reserve, twice what they expected to have. The craft's 44 engines and four computers that drive the engines in orbit worked flawlessly. The cargo bay doors opened and closed just as they were supposed to. The searing reentry through the earth's atmosphere did no damage to the thousands of foamed glass tiles covering the underfuselage of the shuttle to protect it from the heat of friction.

Young said that the temperature of the wings, tail and underbelly of the aluminum fuselage never got hotter than 220 degrees Fahrenheit, even though the heat of friction on the tiles rose to 2,400 degrees and to 3,000 on the nose and tail. This was when the shuttle was at 300,000 feet and moving toward the Earth at more than 24 times the speed of sound.

"We knew the temperatures were out there, we could see the pink and orange glow from all that heating through the cockpit windows," Young said. "They just didn't get into the vehicle; the tiles kept the vehicle cool."

Young said he bounded down the shuttle's stairs after landing so he could see the condition of Columbia's underside where the most punishing heating took place. Said Young: "People had been telling us it was impossible that some of these tiles wouldn't fall off. Well, none of them fell off and those tiles went through some of the roughest ascent and reentry you can imagine."

The two astronauts saved most of their praise for the way Columbia handled during its 5,000-mile glide over the Pacific Ocean to a pinpoint landing in California's Mojave Desert. Young said he could have used the wings, tail and elevons to fly it by himself through hypersonic speed to touchdown.

"There's no way you can compare a vehicle with wings on it to a ballistic body like Apollo or Gemini," Young said. "You move the wings somewhere and they stay there, you move the nose somewhere and it stays there. I think it's possible to fly the whole reentry aerodynamically, this vehicle is a lot more stable than we expected."

Young said he landed Columbia farther down the seven-mile-long runway than he was asked to so he could test the shuttle's wings and tail for lift. Again, Young said the lift he got at landing was remarkable: "We hardly used our brakes. I tell you, that was quite a performance, taking 99 tons out of orbit and getting it back down all in one piece."

During their 75-minute press conference, Young and Crippen showed pictures of the Earth they had taken through the huge cockpit windows of Columbia. Like a spaceborne travelogue, the film took viewers from the deserts of Saudi Arabia to the glaciers of the Himalayas, from the islands off the coast of South Africa to San Francisco Bay. At one point, the film stopped on a picture of Tehran from 170 miles in space.

"We're going to send autographed pictures of this place to 52 of our fellow Americans," Young said, "so they can have keepsakes of their ex-hometown."