Until yesterday, they were "the six other astronauts" who would accompany a celebrated school teacher named Christa McAuliffe when she became the first private citizen to travel in space.

But when the space shuttle Challenger exploded in a fireball over the Atlantic, the nation suddenly became aware of the entire crew, mourning its members, in the words of President Reagan, as "heroes" and brave "pioneers."

Besides carrying the first teacher-astronaut, the shuttle mission was remembered yesterday as having one of the most diverse crews in the history of space travel, including four veterans of previous shuttle flights.

There was engineer Judith A. Resnik, 36, the nation's second woman in space; physicist Ronald E. McNair, 35, the second black American in space; and engineer Ellison S. Onizuka, 39, the first Asian-American astronaut. The other veteran was Francis R. (Dick) Scobee, 46, the flight commander.

There was also rookie astronaut Michael J. Smith, 40, raised near a tiny airport in Beaufort, N.C., where his lifelong dream of space travel was born; and Hughes Aircraft Co. engineer Gregory B. Jarvis, 41, chosen as mission payload specialist from among more than 600 competitors at Hughes, known to friends as an enthusiastic jogger, skier, backpacker, cyclist and classical guitarist.

"It's a tragic loss," said John Turner, associate dean of the graduate school at Massachusetts Institute of Technology, where McNair earned his PhD in 1976. "It was a significant combination of people which really symbolizes what this country is all about -- a diversity of races, sexes and vocations."

Like McAuliffe, all had worked to inspire youngsters to reach for great achievements, even as they piled up accomplishments in their own professions. All were as celebrated as McAuliffe in their own communities. And their towns had responded with the same affection and pride that Concord, N.H., and much of the nation showed McAuliffe.

There was a Judith Resnik Day in Akron, Ohio, after her first flight. There is a Ron McNair Boulevard in his hometown of Lake City, S.C. Onizuka's high school in Kealakekua, Hawaii, held special assemblies when he returned from space, as Auburn High in Washington state did for Scobee -- the sorts of heroes' welcomes the entire nation gave to the first astronauts.

Scobee carried an Auburn pennant into space on his first mission in 1984 and brought it back to the school, where it still hangs. And Smith had planned to carry with him a miniature town flag with the gold seal of Beaufort and to bring it back to the fishing town of 4,500 for a gala reception and high school commencement address in June.

Yesterday, the town flag on the waterfront was flying at half mast. "The town is really in a state of shock," said Beaufort Mayor Joyce Fulford, who had known Smith since his boyhood. "They have been so supportive of Mike in this venture."

The national tragedy was mourned in deeply personal ways by all those who knew the victims or felt a personal connection to them.

Millions of American viewers witnessed the scene at Christa McAuliffe's Concord High School, where 200 pupils and teachers watched in horror as the shuttle exploded. There were no cameras to record a similar scene that took place at Resnik's alma mater, Firestone High School in Akron.

"I hope God will be good. I hope he'll be good to all of us," was all that Concord High principal Charles Foley could say.

Rabbi Abraham D. Feffer of Akron's Bethel Congregation, where Resnik's family worshipped, said at midday that in spite of the televised image of the shuttle disintegrating in midair, the loss was too horrible to accept immediately.

"Right now, we still hold out hope that somehow she may be rescued," he said. "Maybe a miracle will happen. We're human beings, so we keep hoping. We're so confused that we hold onto every straw."

Smith's brother Patrick was more accepting of the mission's fate.

"He worked hard for it, he worked hard for 24 years," he said of his brother. "It was his dream alone. We all have dreams and that was his. He achieved his, and for that we're grateful."

"Nobody in my family has any thoughts about stopping the shuttle program," continued Smith, who had gone to Cape Canaveral for the launch, but returned home to Beaufort after the initial delays. "It's positive for the United States. I think anybody who flies airplanes realizes these things will happen . . . . Sooner or later, we all knew there would be an accident."

For much of the nation, yesterday's tragedy was even more shocking because Americans had come to take space travel for granted -- a contrast to the early space shots when all astronauts were celebrities, and Americans watched every countdown, holding their breath in the moments after each liftoff.

"Greg Jarvis and the others were delighted the teacher was on board because it really gave a little oomph to their launch," said James Straub of Spring Valley, N.Y., Jarvis' father-in-law. "Otherwise it would've been just the 25th launch . . . . They had 24 good ones, and you just assume they're all going to be good."

In fact, Jarvis was scheduled to fly on two of the earlier "good ones," but was bumped, in part to make way for Sen. Edwin Jacob (Jake) Garn (R-Utah) and Rep. Bill Nelson (D-Fla.), who flew on the 23rd and 24th missions.

Those close to the astronauts portrayed them as people who lived to scale heights and break down barriers. McNair, a saxophonist and karate teacher, who often addressed minority groups, was described as an inspirational speaker who implored high school students to "sort of hang it over the edge a bit, take some risks," an acquaintance recalled.

Onizuka returned often to his Hawaii high school, and according to editor Buck Donham of West Hawaii Today, "was just constantly surrounded by kids . . . . He would tell them: hard work, perseverance, all that good stuff."

Resnik, who earned her PhD from the University of Maryland, was vacationing at Bethany Beach when she learned that the space program was being opened to women from reading an ad in an engineering magazine, a friend recalled. She played down her own selection, but the friend recalled: "All her friends knew that if there was going to be a woman astronaut, Judy would be it."

For all the hoopla, the astronauts of the 25th shuttle saw themselves mostly as ordinary people, friends and family said. After winning the Hughes competition, Jarvis told the Torrance, Calif., Daily Breeze:

"You look at an astronaut who is just about a perfect human being and here you are, your hair falling out, and they call you. You're being placed in a position where you are one of a very small set of people who can share this experience."

Yesterday the whole nation experienced a shared sadness. "It's been pretty devastating, almost like the same feeling when John Kennedy was shot," said Terry Phillips, assistant manager of the Holiday Inn in Coco Beach, Fla., where the economy depends on the Kennedy Space Center. Nearby, the Satellite Motel marquee read: "May they rest in peace."