The barge sits just north of Claymont, near the Commodore Barry Bridge, performing work to maintain the depth of the Delaware River's main shipping channel at 40 feet.

The Army Corps of Engineers, which for years has fought to increase the depth to 45 feet, wants to make the most of this situation, and is pressing a federal judge for permission to cut five feet deeper into the river.

Saying it has cleared a final environmental hurdle, corps attorneys last week asked U.S. District Judge Sue L. Robinson to relax her hold on a $300 million project to deepen the river.

Some close to the case rated the federal agency's maneuver a long shot, citing unsettled claims of state and federal jurisdiction and two lawsuits pending in New Jersey.

"In this world, a person can ask anything," said Richard Fleming, a member of the Delaware Nature Society, one of five groups that joined Delaware in seeking a preliminary injunction against the dredging. "I very much doubt that the judge would be influenced" by appeals outside those made in courtroom arguments last month.

Robinson had ordered the corps to hold off work last month pending her decision on Delaware's request for a preliminary injunction barring action without two key state environmental approvals. The judge ordered the hold without issuing or ruling on the formal preliminary injunction sought by Delaware.

"She had not rendered any decision yet on 'yes, you may' or 'no, you can't,' " said Edward Voigt, a corps spokesman in Philadelphia.

Since then, Voigt said, the corps has submitted what it said is a final conclusion that the project would comply with Environmental Protection Agency requirements under the Clean Air Act. Agency officials had previously agreed to delay dredging until its Clean Air findings were complete.

"We were basically letting the judge know that the one constraint that was still in place at the time of the hearing is complete, and we're ready to move forward, pending whatever her decision might be," Voigt said.

Delaware's Department of Natural Resources and Environmental Control has argued that state regulators need to be satisfied with air quality reviews. State officials want the court to issue an injunction blocking work while the corps secures an underwater construction permit and updated approval under federal coastal zone management regulations.

DNREC has promised the corps a prompt decision if the federal agency applies for a new underwater construction permit. Delaware rejected the federal agency's original permit in July after postponing a decision for more than five years.

DNREC and environmental groups have argued that the corps' environmental-impact studies are outdated in some cases, and provide an inadequate picture of risks from toxic compounds now buried along the channel. Congress approved the project in 1992, and the corps completed its last supplemental environmental impact review in 1997.

Critics argue that the corps failed to consider dredging hazards to fish, horseshoe crabs and other aquatic life and habitats -- particularly sturgeon, a large fish now at risk that once supported an entire industry along the river.

Federal officials have insisted that dredging schedules will avoid important fish-spawning seasons, and pointed out that river sediments have been dredged continuously for decades without serious harm.

Robinson pointedly mentioned that state delay during court arguments last month, and pressed the state to explain its actions in light of Congress voting to authorize and fund the project.

The Delaware Riverkeeper Network led a coalition of Pennsylvania, New Jersey and Delaware environmental groups opposing the corps' plan. New Jersey regulators also sided with Delaware, and filed their own suit, citing unresolved environmental protection issues, river sediment contamination and questions about where to dispose of the dredge spoils.

Pennsylvania and the Philadelphia Regional Port Authority are supporting the corps' project, and have business-group backing in all three states, including from the Port of Wilmington.

Supporters argue that the deepening will give Philadelphia and nearby ports a chance to keep and attract shipping traffic as use of deeper-bottomed vessels increases. Deeper water is considered crucial to financing of a huge new container port proposed for a bend in the river between the former Philadelphia Navy Yard and the Packer Avenue terminal.

Critics of the project say the deeper channel won't generate enough traffic to justify its cost to taxpayers and effect on the environment.

A Government Accountability Office review of the corps' cost-benefit statements is expected in mid-March.

Voigt said that Norfolk Dredging Co. already is on the river about a half-mile south of the Commodore Barry Bridge, clearing silt to keep the channel at its authorized 40 feet. The company has an offer, good through mid-February, to increase the dredging depth to 45 feet from north of the Pennsylvania line to a point near the Chesapeake & Delaware Canal.

All of the Delaware River is inside the state of Delaware in that stretch of the waterway.