He faced the sobbing widows and children once again today, as he had after Lebanon, after El Salvador, after Gander. He summoned them once again to look beyond their grief, to believe that the deaths they mourned had not been in vain.

In the days since the seven astronauts of the space shuttle Challenger died in a fiery explosion, President Reagan has struggled to direct the emotions of a grieving nation. Shunting aside other business of state, he has taken to a nationally televised pulpit, offering a message of hope, insisting that some good will come from a terrifying loss.

Today, as he stood in a balmy Texas breeze, his voice heavy with emotion, Reagan bade farewell to "our seven star voyagers" but again called the nation to look beyond defeat.

"Man will continue his conquest of space," he declared. "Sometimes, when we reach for the stars, we fall short. But we must pick ourselves up again and press on despite the pain."

Reagan has mourned soldiers and sailors killed in service to the nation. He paid tribute to U.S. servicemen who died in their sleep in their Lebanon barracks, to the Marines killed at a sidewalk cafe in El Salvador, to a Navy diver slain by terrorists, to Army peace-keeping soldiers who died in a Canadian plane crash.

But today was different. He came not to honor members of the military killed while defending the nation but to pay tribute to explorers. They did not die in a hail of gunfire or at the hands of a suicide bomber "I wish there was something I could say to make it easier, but there just aren't any words." -- President Reagan but rather in a risky experiment in technology.

Among them, Reagan noted, was a teacher, Christa McAuliffe, who "captured the imagination of the entire nation, inspiring us with her pluck, her restless spirit of discovery . . . . "

The president reached back in American history to explain the grief and triumph of explorers.

"We think back to the pioneers of an earlier century, the sturdy souls who took their families and their belongings and set out into the frontier of the American West," he said. "Often, they met with terrible hardship. Along the Oregon Trail, you can still see the grave markers of those who fell on the way. But grief only steeled them to the journey ahead."

"Today, the frontier is space and the boundaries of human knowledge," he said. "Our nation is indeed fortunate that we can still draw on immense reservoirs of courage, character and fortitude, that we are still blessed with heroes like those of the space shuttle Challenger."

As thousands of National Aeronautics and Space Administration workers clung to each other and wept on a grassy mall near the control room where Challenger's explosion was monitored, Reagan renewed his commitment to future space voyagers.

He recalled Ronald E. McNair, "who said he learned perserverance in the cotton fields of South Carolina. His dream was to live aboard the space station, performing experiments and playing his saxophone in the weightlessness of space. Ron, we will miss your saxophone, and we will build your space station."

Reagan has adopted the space program as one symbol of his vision of a nation with limitless ambition. He went to California to watch a shuttle landing, he campaigned at high-technology centers, he telephoned all of the previous shuttle astronauts from the White House and once from a campaign train.

As he led the nation in mourning today, Reagan tried to instill hope in the grieving space workers massed before him.

"The dedicated men and women of NASA have lost seven members of their family," he said. "Still, they too must forge ahead, with a space program that is effective, safe and efficient but bold and committed."

Reagan, by nature a man who does not dwell on defeat but celebrates optimism, gracefully shouldered the difficult task of comforting the survivors of tragedy today, as he had done in a cold rain at Camp Lejeune, N.C. and in an airplane hanger at Fort Campbell, Ky.

With First Lady Nancy Reagan, he met with the widows, widower, and children of the seven astronauts in a barren classroom at the NASA Avionics building. They stood in a semicircle around him. Erin Smith, daughter of the shuttle's pilot, Navy Cmdr. Michael J. Smith, clutched a brown teddy bear with a pink apron.

"I wish there was something I could say to make it easier," he told them, "but there just aren't any words."