For half a century, the Pentagon has represented the heart of U.S. military might. But for the soldiers and civilians who began working there when it opened, the world's largest office building has always been something more personal.

To Frederick and Opal Belen, the drab building with 17 miles of corridors is a place that spawned a romance that still endures. To Wilhelmina Burch Gibboney, it is one of the first places where she saw integrated cafeteria lines and restrooms. And to Ed Pavlick, one of only two original employees still working at the Pentagon, it is a onetime engineering wonder that through neglect has fallen on hard times.

Yesterday, in a ceremony to mark the Pentagon's 50th anniversary and declare it a national historic landmark, about 20 of the Pentagon's original employees joined top military leaders in honoring the building and those who have worked there during war and peace.

"In its own solemn and unpretentious way, it has withstood time," said Gen. Colin L. Powell, chairman of the joint chiefs of staff. "But even though we talk about it as a living thing, even though the media quotes it as a living person, I hope no one will forget that the Pentagon really is the thousands of people who work in its offices."

The original employees were among hundreds of current and former Pentagon employees at the ceremony. Two of the originals -- Pavlick and switchboard supervisor Marian Bailey -- still work there.

The Pentagon was constructed in a 16-month rush at the beginning of World War II and officially opened in January 1943, though many employees began working in sections of the five-sided building several months earlier.

"The construction was completed in 16 months. That truly is a remarkable feat," said Defense Secretary Les Aspin. "Today, the environmental impact statements would take twice that long."

Several of the original workers recalled having to cross muddy fields on wooden planks to get inside and said they worked in the midst of an active construction zone.

Frederick Belen, a security officer at the time, said he used shipping tags as makeshift building passes for employees because official passes were not available. And the need for construction and other workers was so desperate that many of those hired were security risks.

Once, Belen said, he ordered a shakedown of the building's 800 cleaning workers and filled several bushel baskets with weapons, mostly knives. "After the war started, everybody was gobbled up by the other departments. Normally, you'd fire somebody with a weapon, but we couldn't. We had to have someone clean the building."

Belen and his wife met on a double date on Feb. 7, 1942. Then, after both were transferred to the Pentagon, they commuted there together each day and cemented their romance. The Belens, who live in Arlington, married exactly a year after their first date and celebrated their own 50th anniversary three months ago.

Another original worker who returned for yesterday's ceremony was Gibboney, 94, who wrote a safety newsletter for ordnance workers.

Gibboney, who is white, said that the Pentagon's cafeteria lines were segregated when it opened but that First Lady Eleanor Roosevelt insisted they be integrated after a racially motivated fight broke out in the building's first months.

Another vestige of the building's construction under Virginia's segregationist Jim Crow laws remains, however. The building had twice as many bathrooms as needed so that blacks and whites could have separate facilities. Today, they are used to separate smokers and nonsmokers.

The structure no longer is the engineering marvel it once was, Pavlick said. Its central air conditioning and road system were unique in 1943, he said, but time and neglect have taken their toll.

"The building was way ahead of its day when it opened," said Pavlick, who is director of building management services. "Today, all the systems are antiquated. It's in pretty bad shape."