Tek Saidha strolled out of the King Street Metro station last Thursday morning and did what came naturally. He walked around the orange-vested bricklayers and past the idling backhoes, then darted across Duke Street toward the U.S. Patent and Trademark Office.

After six months of crossing the hectic thoroughfare that way, it never occurred to the 52-year-old Saidha that the long-delayed pedestrian tunnel under Duke Street might be open for use.

"It's open?" Saidha, a patent examiner from Burke, asked as he crossed the street, looking over his shoulder toward construction workers toiling away near the tunnel. "It doesn't look open."

It had been, for a few hours at least. At 6 a.m. July 1 -- six months later than originally planned -- the 170-foot-long, 20-foot-wide and 12-foot-high concourse was quietly opened to the thousands of employees now working at the massive PTO complex and other pedestrians who had been forced to brave the Duke Street crosswalk.

"It's safe and it's sound, and I think the general public will enjoy the convenience of using it," said Alexandria Mayor William D. Euille (D).

The $3.5 million brick-lined tunnel runs from the southern end of the King Street Metro station under Duke Street and onto a plaza near the partially finished PTO complex. Last week, some pedestrians spotted the still-heavy construction around the concourse and, assuming the tunnel was not yet usable, crossed above ground. Others ambled into the tunnel, making it to the other side of Duke Street without looking left and right.

"You don't have to risk your life crossing the street," said attorney Kim Knur, 38, of Alexandria as she walked through the tunnel to the Metro station.

Construction of the PTO complex has long been one of Alexandria's most divisive development projects, and the tunnel's opening ended only one chapter of the story. The saga started in 2000, when the city was awarded the 2.3 million square feet of government offices. Critics predicted the complex's 7,100 employees would mean traffic nightmares for an already-congested area at the edge of Old Town. To encourage workers to use Metro, the city required the project's developer, Carlyle Development Corp., to build the tunnel.

The tunnel was scheduled to open in December, when 2,600 employees moved into the first phase of the PTO complex. But Carlyle did not start construction on the tunnel until October, delaying its completion by half a year.

The setback outraged local activists and some city leaders, who disagreed on who was to blame. Neighborhood organizations claimed the city failed to monitor the project and demanded an investigation. The city accused Carlyle of poor planning. Carlyle said it had misjudged the complexity of the project.

To the dismay of activists, the city did not fine Carlyle or its subcontractors for the delay but did let the PTO employees occupy the building even though the tunnel was unfinished. For the next six months, the company transported employees on shuttle buses to and from the Metro station.

The opening was a relief and a bit of a surprise, said Vice Mayor Redella S. "Del" Pepper (D). The day before it was scheduled to open, the tunnel looked like it would "take a miracle" to finish, she said.

"We're very pleased," Pepper said. "Sometimes you just have to forget about who's responsible."

Workers are putting the finishing touches on brickwork and on a staircase to the tunnel, said Emily Baker, an engineer with the city's Department of Transportation and Environmental Services. Except for some landscaping that must wait until cooler fall weather, the tunnel will be completed in time for the July 17 dedication ceremony, she said.

The five-building, 15-acre PTO campus is scheduled to be completed in 2005.

For critics of the PTO development, the finished tunnel does not equal a resolution. The delay -- and the city's decision not to discipline Carlyle -- shows that the city bends to the will of developers, said Frank Putzu, president of the Seminary Hill Association. And, he said, the tunnel does not guarantee the PTO will not add to the city's traffic woes.

"What remains to be seen is whether 50 percent of all their employees and guests take the Metro," Putzu said, referring to city estimates of the percentage of PTO employees who will use public transportation.

Saidha said many of his co-workers have switched to Metro since moving from the old PTO buildings in Crystal City. Asked whether he would use the tunnel that evening, Saidha said he would do his best to remember.

"Hopefully," he said. "I think it's safer."

Office workers use the PTO pedestrian underpass, which opened last Thursday, six months later than planned.Some pedestrians didn't realize the tunnel was open, instead daring to cross Duke Street above ground. "It doesn't look open," one walker said.Construction workers apply finishing touches to the 170-foot tunnel as pedestrians use it to cross under Duke Street.