Pennsylvania's top agency for historic preservation is calling for additional archaeological work at the Delaware River site of the proposed SugarHouse casino.

The Pennsylvania Historical and Museum Commission recommended in a letter on Wednesday to the Army Corps of Engineers that more work was needed in an area believed to be the site of a British fort from the Revolutionary War.

The commission's remarks were part of a review process being led by the corps for a permit to allow the casino developer to build into the water. The commission is a main consultant to the corps.

Douglas C. McLearen, chief of the commission's division of archaeology and protection, also said in the letter that the corps should not allow building until all of the commission's recommendations are addressed or resolved.

Leigh Whitaker, a spokeswoman for SugarHouse, said the company was evaluating the commission's recommendations. She said a consultant hired by SugarHouse - A.D. Marble & Co. - began investigating the site's historic significance more than a year ago.

She said the consultant had not found any physical evidence of a fort, although maps "lead us to believe it existed."

"We have uncovered some Native American artifacts and some foundations, consistent with residences from the 1800s," she said.

The commission is urging a far deeper level of investigation. It is recommending not only further testing for the possibility of a fort - identified as British Redoubt No. 1 - but also additional investigation of landforms. In December 2006, the SugarHouse site, on the riverfront in Fishtown and Northern Liberties, was one of two locations selected for Philadelphia's first slots casinos.

But the project has yet to begin construction, stalled by court challenges, opposition from City Council, and protracted reviews for permits.

McLearen said the purpose of the additional work is to gain a better understanding of the historic shoreline, as well as any buried historic or prehistoric ground surfaces.

Under the Clean Water Act, the corps has to issue a permit before SugarHouse can build into the water. As part of the review process, stakeholders - including residents and archaeological experts - are allowed to participate in a public comment period that ends Friday.

Hilary Regan, a resident of Northern Liberties who has commented to the corps on the historical significance of the area, called the recommendations of the commission "appropriate and fair." "There are a lot of potential artifacts here and a lot of history that we can learn about," she said.