It was a last-minute addition, almost an afterthought.

But against virtually all expectations, the archaeological excavation of the President's House, now more than two months running, has uncovered powerful physical evidence evoking presidents and slaves, eliciting excitement and deep interest from the thousands who have packed the public observation platform to view the site at Sixth and Market Streets.

In response, the city and Independence National Historical Park have extended the dig through July Fourth. It had been expected to wrap up about now.

"We want to take advantage of all the interest," said Joyce Wilkerson, Mayor Street's chief of staff.

"This is a national story," directly related to July Fourth, she added.

At the same time, the city and park face an extraordinary conundrum: what to do next.

Should the dig and its findings simply be filled in and the long-awaited memorial to the President's House and its residents proceed as planned? The house was where George Washington and John Adams created the presidency in the 1790s. And it was where Washington quartered at least nine slaves as he helped launch modern democracy.

Or should the findings - which include Washington's great bow window and the foundations of the kitchen and an underground passageway, the subterranean world of slaves - somehow remain accessible, open to view?

What U.S. Rep. Bob Brady saw Friday when he visited unannounced, almost anonymously, left him nearly speechless.

"I was completely shocked," he said in an interview later in the day. "I never thought anything like this would be there. I looked at it, and there was the oval window and the passageway. How can you cover that up?"

"I'll tell you one thing," he continued. "We need to stop and rethink what we're doing there. . . . Damn! I got chills."

The city and the park, partners in the project, are discussing the matter, officials said. And every option is on the table, Wilkerson emphasized, noting that decisions should be made in a matter of weeks.

"We're asking all the questions," she said. "None of us has the answers yet. None of us anticipated the findings. I think when you stand and look down at the archaeologists working, it's hard not to be drawn in."

The first question, she added, is what is generating the excitement: "Is it the hole? Is it the excitement of the discovery? Is it the opportunity people are having to see archaeologists at work?"

For visitors, all those issues may come into play. But what is heard over and over on the viewing platform as blacks and whites, Philadelphians and out-of-towners gaze down at the network of walls and stones are expressions of awe:

This is the actual foundation of the curved bow window that was the antecedent to the oval rooms and ultimately the Oval Office in the White House. This is where Washington stood to greet dignitaries and the public.

Steps away are remains of the actual room where slaves, including Washington's renowned chef, Hercules, labored - hidden from those upstairs.

"It's the real deal," one visitor said in a typical comment: democracy and America, the good, the bad and the ugly.

Wilkerson said an oversight committee appointed by Street to keep tabs on the project will meet again Tuesday to talk.

"We're trying to figure out how to get the issues framed with enough information so that the decisions can be made about how we proceed from here," she said. "What does it mean to keep [the excavation] open? Just keep it open? Or do you keep it open and preserve it in some way, protect it? What does protect it mean? Can you incorporate it into a design? What does that mean to the competition that we had that was pursuant to a public process?

"We're just examining all those issues. We haven't made any final decisions. There's not a single opinion. On the oversight committee, not everybody feels the same way."

Kelly/Maiello Architects & Planners, which won the design competition to create the commemoration, did not foresee incorporating archaeological findings into a memorial. Nor did any of the other bidders for the $4.5 million project.

Emmanuel Kelly, principal of the Philadelphia design firm, said last week that "everyone agrees that what has been discovered is very valuable."

He declined comment beyond that, except that "we're waiting to be given some direction" by the city and the National Park Service.

Several participants at a meeting about 10 days ago said Kelly had argued that incorporating archaeological findings would add substantially to the cost of the memorial.