(Updates with federal advisory on bridge construction)

By Benno Groeneveld

MINNEAPOLIS, Aug 8 (Reuters) - A week after a deadly bridge collapse, U.S. Navy divers cut through tangled debris with underwater torches and saws on Wednesday in the search for victims, while investigators identified a possible flaw in the 40-year-old span's design.

The Aug. 1 rush-hour collapse of the Interstate 35W bridge hurled vehicles into the Mississippi River 65 feet (20 meters) below, with many tumbling onto the bridge's crumpled concrete deck.

In response, officials demanded inspections of potentially suspect bridges across the United States amid renewed calls to shore up the country's aging infrastructure.

Five people were killed in the bridge collapse, a death toll that was confirmed within a day of incident. Eight other probable victims are listed as missing.

The recovery process has been slowed by huge slabs of steel-reinforced concrete and dangerous chunks of debris submerged in the river's swift, turbid waters. In some cases, divers had to use their fingertips to read license plates.

"This is going to be a process of having to, most likely, pull these vehicles out and do a long-term extraction, taking apart the vehicle to recover evidence, (and) any (human) remains," Minneapolis Police Capt. Mike Martin told reporters.

National Transportation Safety Board investigators said they found a potential design problem with gusset plates, steel plates that tie together angled steel beams of the bridge's frame.

WEIGHT OF CONSTRUCTION EQUIPMENT

Investigators are trying to verify loads and stresses on these plates at specific locations as well as the materials used to construct them.

One possible stress may have been the weight of construction equipment and materials on the bridge when it collapsed, the U.S. Transportation Department said in a statement on Wednesday.

Safety board and transportation officials said the increased focus on steel plates is preliminary. They would not say exactly where they were located on the bridge or whether their failure alone would have caused the collapse.

"We are continuing to make progress on this investigation, and each area of inquiry gets us closer to ultimately determining the cause of this tragedy," safety board Chairman Mark Rosenker said in a statement.

Federal transportation officials were concerned enough with the NTSB finding to issue an advisory to states to "carefully consider" the weight of construction equipment used in bridge projects.

Out of some 100 people injured, only a handful remained hospitalized. One person is in critical condition.

For the families of the missing it has been an agonizing wait. Members of Minneapolis' large Somali immigrant community are grieving over the presumed death of a 23-year-old nursing student, who was pregnant, and her 2-year-old daughter.

Minnesota officials were quickly laying the groundwork for replacing the vital eight-lane bridge, which was the state's busiest. About 140,000 vehicles crossed the bridge every day.

Construction bids were due on Wednesday and officials hoped to choose a contractor within weeks to build a new bridge by the end of 2008, with the help of $250 million promised by the federal government.

(Additional reporting by John Crawley in Washington)

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