Two American astronauts flew the rocketship Columbia back home from the black seas of space today, the first time that men have landed a winged spacecraft on earth like an airplane.

"We just became infinitely smarter," astronaut John W. Young said after rolling the Columbia to a dusty stop near the end of a seven-mile-long runway in the Majave Desert.Boomed astronaut Robert L. Crippen, Young's copilot on their 54 1/2-hour flight around the earth: "This is the world's greatest flying machine. It was super."

Ending an American drought in space of almost six years, Young and Crippen opened a new era in space travel with a flight that began at Cape Canaveral and took them around the world 36 times to a pinpoint landing 100 miles northeast of Los Angeles.

Three years late and almost $2 billon over cost, the shuttle proved to be the returnable and reusable machine it was built to be.

Looking as if he had done nothing more taxing than fly across the country. Young -- so anxious that he didn't wait for the crew physician to board the spacecraft -- bounded down the steps from the cockpit and slapped the outstretched hands of his waiting colleagues.

He flashed a thumbs-up sign and inspected the shuttle.

Crippen waited on board for the doctor and emerged from the craft a few minutes later, and the astronauts boarded a van that took them to a nearby dispensary.

At a brief ceremony about an hour later, the veteran Young said that "this is the best thing that ever happened to me. This was a tremendous mission from start to finish."

Beamed rookie Crippen: "Waiting 12 years for this fight was worth it. 'I'd wait in line another 12 years but I know I won't have to wait that long anymore. We're back in the space business to stay."

Said NASA's acting administrator, Alan Lovelace: "This flight proves again that the U.S. is number one . . . number one."

That was the theme heard all day long here at Edwards Air Force Base, where Columbia will land at the end of three more test flights this year and next. The next test flight will be in late September.

When the test flights are over, the shuttle "goes operational" in late 1982, makes seven flights in 1983, many as 17 in 1984, 24 in 1985 and 30 in 1986. The shuttle's job is to truck all the U.S.'s civilian and military satelites into orbit for the next 20 years and do it at a fraction of the cost for conventional rockets. Its flights cost about $32 million compared to $100 million for the least costly Apollo flight.

Columbia's cargo bay is booked solid through the first 52 flights.

If any maiden space flight of any new spacecraft could ever be described as flawless, the flight of Columbia would come close. Young and Crippen took the 75-ton Columbia into orbit to test its cargo bay doors, its maneuvering engines, its four navigating computers and the 30,759 foamed glass titles that cover its fuselage to protect it from the scorching heat of re-entry. It all worked. Everything hapened the way it was supposed to, as if a Hollywood producer had written the flight plan.

The most critical concern was the titles, which were developed at a cost of more than $300 million to protect the shuttle's aluminum air frame from reentry heat.

In some places, even the loss of one tile might cripple Columbia if a hole burned through the craft and damaged the shuttle's navigation system or the hydraulics that control the craft's elevons and landing gear. Not a single critical tile appeared to be lost when Young and Crippen taxied Columbia to a stop just before 1:30 p.m. EST.

The only tiles lost were those on top of the rear engine pods that Young discovered to be missing after liftoff on Sunday and which were not critical to entry.

Another major worry was the deadstick landing of the craft, which is the size of a DC9. It weighed 150,000 pounds upon landing, compared to the 200,000 pounds it weighed fully fueled at launch and to a DC9's maximum landing weight of 128,000 pounds.

The return to earth began today at the end of Columbia's 36th orbit over the South Indian Ocean, where Young and Crippen turned the shuttle upside down with its tail and engines facing aft. Firing the engines to slow the spacecraft, Young and Crippen began to fall rapidly out of their 70-mile-high orbit.

Turning the shuttle right-side-up, Young and Crippen flew over Guanm just before punching through the earth's atmosphere and temporarily losing communication with the ground crews. All returning spacecraft suffer radio blackouts just after re-entry when the air around the spacecraft gets so hot it creates electrified gases that block out radio signals.

When Columbia slowed enough to come out of radio blackout, it was at an altitude of 165,000 feet about 500 miles off the California coast and moving at 10 times the speed of sound. The shuttle's computers had done their job flawlessly.

"What a way to come to California," Young said.

A few minutes later, Crippen radioed to Houston, "That was the neatest thing in the whole world."

Approaching north of Monterey Bay at Mach 7 (seven times the speed of sound), Young pitched the winged paceship down so he could begin to use the elevons and the three-story-high tail to navigate and get a better look of the lay of the land ahead.

"Columbia, you're coming right down the chute," Mission Control's Joe Allen said as the astronauts swung down toward Edwards Air Force Base. On the large display board in the control room, a blue line plotted the path Columbia was to follow to the ground, and a parallel red line steadily traced the craft's actual path, first above the blue line, then below it, then above again.

When Columbia crossed over Edwards, it was at 50,000 feet and still out of sight of the naked eye but made its presence known to the approximately 500,000 people who'd come to the desert with two loud sonic booms that sounded like two giant claps of thunder. At the sound of the booms, the crowds at Edwards cheered as they would the winning homerun at a baseball game.

Making a wide banking turn toward the left, Young and Crippen were followed by four T38 jets serving as chase planes. Suddenly, television cameras aboard one of the chase planes showed Columbia moving toward a landing, its nose moving up and the black-and-white shuttle outlined against the brown and parched mountains of the Sierra Madres.

Down it came, as majestic in flight as it had been at liftoff two days and six hours before. The black wheels touched first, kicking up dust from the dry lake bed that serves as Rumway 23 here.

Then, the nose wheels came down and kissed the dust as if the landing had been practiced a thousand times. Speed brakes extended, Columbia slowed almost immediately from more than 200 miles an hour to 20. Moments later, it came to a stop about two miles short of the end of the seven-mile runway.

"Do I have to take it to the hangar, Joe?" Crippen asked jokingly, knowing Columbia has no power to maneuver in the atmosphere or on the runway.

Replied Allen: "No, we're going to have to dust it off first."

Said Young: "Can we come out now?"

Answered Allen: "You're going to have to get your bags off first. But don't forget to verify that you've got your baggage tags. . . ."

Donald K. (Deke) Slayton, orbital flight test manager, said that while it is too early to know whether future flights will be accelerated, the Columbia's performance might make it possible to drop one of the last test flights from NASA's schedule.

Slayton also noted that the successful first flight of the problem-plagued shuttle might help NASA to squeeze more money out of the administration and Congress. "I have to expect that this will help us rather than hurt us," he said. "We were at the point [in the program] where we had to produce, and I think we did."

Young and Crippen had just written a script for a new epoch of the Space Age.

In the next five years, communications satellites, navigation satellites, and data transmission satellites will be carried into orbit by the shuttle. RCA, Bell Telephone, Satelite Business Systems, Hughes Aircraft, the countries of Saudi Arabia, Canada, Indonesia and the People's Republic of China are just a few of an estimated 50 customers who have already booked space in the 60-foot-long cargo bay of the shuttle.