John Walsh was struggling as he told the painful story once again, how his 6-year-old son Adam was abducted from a shopping mall in Florida.

Adam was just three aisles away from his mother that day in 1981, Walsh said. A serial killer with a preference for blond boys was stalking his prey at the mall.

"I almost couldn't get through it at the end," Walsh, 53, said of his remarks last week. "It brought back a lot of memories."

Walsh, with his wife, Reve, 48, at his side, had been addressing a crowd at the dedication of the National Center for Missing and Exploited Children's new home in Old Town Alexandria.

More than anything, Walsh wanted to convey the frustration and anger he and his wife felt in 1981, a time when there was no system in place for finding missing children.

After Adam's body was found two weeks later in a canal more than 100 miles from home, the Walshes devoted their lives to changing the system. In 1984, Congress mandated the National Center for Missing and Exploited Children, a private, nonprofit organization working in cooperation with the Department of Justice. Since it opened, the center has helped recover 47,284 missing children.

Walsh, a co-founder of the center and host of TV's "America's Most Wanted," looked out at the crowd gathered for the dedication, which included FBI Director Louis J. Freeh, retired Army Gen. Colin L. Powell and Rep. James P. Moran Jr. (D-Va.). Many agencies of which Walsh had been most critical in the past are now among the center's biggest supporters.

Said Walsh, his voice faltering: "This is a building of hope."

Inside the National Center for Missing and Exploited Children, Glenn Miller is studying a photograph of a 6-year-old girl named Diana Cortes who was reported missing in Mexico eight years ago.

Still clinging to hope that Diana will be found someday, her family has turned to the center in Alexandria for help. Because no one knows exactly what she would look like today, Miller is altering an old snapshot of Diana on his computer--in effect, aging her--in the hopes that someone could still recognize her.

"We're going from 6 to 14," said Miller, an age-progression specialist. "Our goal is to create someone who looks like that missing child."

Miller says that most of a person's identity is "in the eyes," and he is using photographs of the child's parents as a guide. Although not 100 percent accurate, the art of age progressing has helped identify children missing for long periods of time.

Center officials said that moving from their smaller quarters in Arlington to the 76-year-old building in Old Town with its 63,000 square feet will help them expand their search for children. The 1999 operating budget is $22,175,000, nearly half of which comes from donations, and the center also will serve as world headquarters for the newly formed International Centre for Missing and Exploited Children, they said.

Charles B. Wang, chairman and chief executive of Computer Associates International Inc., whose donation of $5 million in funding and technology enabled the move to Alexandria, said he hopes the center will serve as the "nerve center" for reuniting families around the world.

Already, the recovery rate has improved from 60 percent in the 1980s to 93 percent today, said Ernie Allen, president of the national center. He attributes the dramatic improvement to "one word: technology."

Disseminating information about a missing child used to take days or weeks, but it now can now be done "almost instantly," greatly increasing the chance of finding a child before harm is done, Allen said.

"I truly believe technology has changed the way we search for missing children," Allen said.

The center is the only organization operating a 24-hour, toll-free national hot line (1-800-THE-LOST), and it has handled more than 1.3 million calls, Allen said. Last year, the center also became the "911" for the Internet, with its new CyberTipline (www.missingkids.com and www.cybertipline.com), which receives leads regarding child exploitation online, he said.

"If your child disappears today," Allen said, "you're not on your own."

Nearly two decades ago, when John and Reve Walsh flew to Washington to ask for help from their U.S. senator, their cabdriver passed one building after another, each dedicated to all kinds of causes.

Reve Walsh asked the driver, "Can you take us to the Children's Building?" hoping there was some organization in the nation's capital that could help her and other families of missing children.

Now there is one in Alexandria. Families of missing children have a building of their own at 699 Prince St.: the Charles B. Wang International Children's Building.

"I couldn't sleep the night before the dedication," John Walsh said. "It was just so emotional for me and Reve."

Adam would be 24 now, his father said. And he has three siblings--Meghan, 17, Callahan, 15, and Hayden, 5.

"Hayden looks just like Adam," his father said. "It's like a joyous reminder."