Dwarfed by historic rockets and spacecraft in the Air and Space Museum's Space Hall, tour guide Robert Stephens stood before a television monitor yesterday morning to watch America's latest space shuttle launch, one of dozens he had seen from this unique setting.

But what started off as a normal launch turned into a disaster, "a terrible thing to see," said a shaken Stephens, a museum volunteer who, with about 30 other persons, watched the shuttle lift off.

Whether they were among the few who saw the shuttle launch live or later turned on radios or televisions after hearing of the tragedy, Washington area residents reacted similarly as this special space mission -- distinguished by having the nation's first teacher-astronaut on board -- disintegrated.

The shuttle explosion, which was broadcast and rebroadcast throughout the day, was particularly heart-wrenching for those watching at the Air and Space Museum, where a special exhibit had been designed around yesterday's launch.

A sign next to the television monitor listed the date for the launch of the Challenger shuttle, the date of its expected return, its seven crew members and an announcement that the museum would be broadcasting teacher Christa McAuliffe's "Live Lessons From Space" on Friday.

Museum officials said they would open a memorial exhibit about the crew by this afternoon.

Accustomed to routine, uneventful shuttle launchings, people at the museum and elsewhere suddenly were transfixed in front of television sets showing a different story.

"I was watching it from liftoff to explosion," said a subdued Linda Owens, an administrative assistant at City Hall in Alexandria. "And I kept thinking, 'Oh, my God, this is real. It's not a space movie.' "

Word of the explosion spread quickly. Local governments, state legislatures and congressional sessions interrupted their meetings; many paused for a prayer or a moment of silence. Media and government offices were deluged with telephone calls for more information.

Those who followed the space program closely, even those who weren't even aware another shuttle launch was scheduled, expressed grief for the shuttle crew and sympathy for the astronauts' families, especially for McAuliffe's husband, her two small children and her parents, who watched the launch from Cape Canaveral, Fla.

On Capitol Hill, the House of Representatives interrupted its session and the chaplain delivered a prayer for the astronauts.

Rep. Steny Hoyer (D-Md.), his voice cracking and his eyes red, paid tribute to McAuliffe in a short, emotional speech on the House floor.

"The best teachers convey the excitement about learning to students, and Christa had that excitement," said Hoyer, who said McAuliffe would have agreed that space exploration is worth the risks.

McAuliffe's husband, Steve, was a law clerk in Hoyer's office in the early 1970s before Hoyer came to Congress. Christa McAuliffe got her master's degree from Bowie State College and taught school in Prince George's County, in Hoyer's district, for eight years.

Recalling a speech she gave to a group of county teachers last summer, Hoyer said McAuliffe was thankful to be part of the space effort and had said then, "I touch the future. I teach."

McAuliffe had never expressed any fear about the flight, Hoyer said, just excitement.

In Maryland, Gov. Harry Hughes issued a statement of sympathy for the families and friends of the Challenger crew.

News of the disaster shocked local officials in Montgomery and Prince George's counties, with each jurisdiction interrupting county council business for a moment of silence.

But in Prince George's, where council members were embroiled in a heated argument over the fate of Metrorail in the county, the political respite was a brief one. The moment of silence passed, and the members resumed their discussion with the same vehemence.

At the National Aeronautics and Space Administration office in Southwest Washington, some of the 50 employes who watched the launch live in the agency's auditorium broke into tears after the awful bright flash appeared on the screen.

"There was numbness," said Barry Haworth, a NASA budget analyst. "You could obviously see the explosion. The camera had gone in for a close-up shot from the chase plane. There was a flash and some smoke, then all you saw was vapor. It didn't take too long to sink in that the orbiter the spacecraft was gone."

Agency employes later gathered in the hallways, adorned with photographs and drawings of other space flights and shuttle liftoffs, to exchange information and console each other.

The sense of loss was very personal, one official said.

"We conduct tests and research and prepare for everything possible," said Walter Steiner, a program analyst in the aeronautics and space technology division. "It's difficult for people to realize, but we are constantly pushing the limits of knowledge. Apparently, there was something here we didn't know."

But Steiner, a former Navy test pilot, said he hoped the agency "is allowed to do what it does best: push back the frontiers of space and knowledge."

At the Air and Space Museum, tourist Patrica Kammer of Buffalo, who had just learned of the shuttle accident, said such tragedies have not dampened her interest in some day traveling in space.

"Yeah, I would still go," she said.