A key assessment of Delta levees that could lend support for a controversial canal around the region is so flawed that its conclusions are essentially useless, according to a panel of scientists.

In surprisingly harsh language, the review found that the long-awaited report from the state Department of Water Resources must be overhauled before it can be used. It also noted that the report's authors dismissed valid concerns about their work in the past.

The panel "believes strongly that the inadequacies in some of the analyses may lead policymakers and others to erroneous conclusions and inappropriate decisions," according to the Aug. 23 report, obtained this week by the Times.

At issue is the Delta Risk Management Strategy, a two-part, $10 million study paid for with state bond proceeds. The first phase is meant to assess the vulnerabilities of Delta levees and the economic and environmental impact of floods. The study's second phase is expected to present options to address the threats identified in the first phase.

The strategy report was supposed to help inform a comprehensive "Delta vision" plan that was ordered by Gov. Arnold Schwarzenegger and is due at the end of November. The scathing review now casts serious doubt on whether that will happen, though officials said the report could still be useful when an implementation plan for the Delta vision is developed next year.

Many observers say the state's water agency has been angling to get a Peripheral Canal built around the Delta and that the "dreams study" strategy report would help build that case by showing how vulnerable the levees are to floods, which could damage Delta farms and threaten part of the state's water supply.

The thinking is that if the water supply from the Delta, which is used by two-thirds of Californians and on millions of acres of farmland, is highly vulnerable, and if shoring up levees is prohibitively expensive, then a canal might appear to be a good alternative.

Few dispute that the Delta is vulnerable, that levee failures could have severe statewide consequences or that shoring up levees would be expensive. But the more acute the threat, the more attractive a canal might appear.

The science review did not specify whether the report's errors tended to skew conclusions in any particular direction, and a state water official strongly denied there was any bias toward a canal in the study.

"What we're interested in doing is seeing as objectively as possible how vulnerable the Delta is," said Les Harder, a deputy director of the water resources department. "We've approached this very openly and very honestly."

The study is one of several under way that address the question of how water should be moved through the Delta region. There is widespread speculation that state officials are trying to build support for a canal through those processes.

In addition to the risk study, groups of scientists and policymakers are drawing up a new Delta vision, writing a comprehensive plan to address endangered species in the Delta, and doing a formal re-evaluation of the way water is taken out of the Delta.

"The DWR (Department of Water Resources) is the common element in all these things and has been trying to force all these studies through the same mold," said Tom Zuckerman, a member of strategy report's steering committee and special projects manager for the Central Delta Water Agency.

"I don't think there is any question this has been orchestrated," he added.

Depending on how it is built and regulated, a canal could deprive the West Coast's largest estuary of fresh water at great cost to the region's water quality and possibly to native fish and other wildlife.

The June draft of the report made a strong case that the Delta could not be relied upon for water deliveries to users across the state, calculating a 28 percent chance of more than 30 levees failing simultaneously in the next 25 years because of an earthquake and as many as 260 floods in the next 100 years.

But the science panel's review said the report's numbers cannot be trusted, saying the results are "of limited utility" and that the study's shortcomings will not be simple to solve.

"We understand the time pressures that have been placed on the ... analysis, but the results are too important and potentially too useful to be rushed to the point that the results are not trusted or that the generated results are unjustified," the panel wrote.

State officials said the criticisms will be addressed and added they did not expect changes to the overall conclusion -- that the Delta is vulnerable and that the cost of it failing is catastrophically high.

"Overall, even given the overly critical scientific review, it's not a fatally flawed document," said Keith Coolidge, a spokesman for CalFed, a state agency that oversees Delta issues.

One member of the governor's Delta vision task force said the crisis facing the Delta is nothing new, but the state's water agency should put the estuary's health on equal footing with the state's water supply.

"Clearly, they have gone back to the Big Ditch approach," said Sunne Wright McPeak, a former Contra Costa County supervisor and member of the governor's Delta vision task force.

Besides a canal, other options under consideration include reducing the state's reliance on the Delta for water, and an idea that couples continued delivery through the Delta with a smaller aqueduct around it.