They suggested Friday that the 390 questions posed by regulators in a leaked draft of the notice of proposed rulemaking and banking industry concerns about some elements could make the proposal more "a work in progress" than a final rule and that lobbying on what gets into the final version could be intense.

"It is very general and very vague," said Kevin L. Petrasic, a partner in Paul Hastings LLP who advises banks and financial firms. He said the proposal offers few details about exactly what is banned along with its requirement that banks demonstrate they aren't engaged in proprietary trading, and could force banks to spend significant money to demonstrate compliance.

American Bankers Association executive vice president Wayne A. Abernathy called the proposal so complicated as to be next to impossible for banks to work with.

"It's a real problem for any bank trying to decide what business to be in. The approach is, 'We don't want you to do anything bad,' but 'Not all investing is bad,' but 'if you make a mistake we are going to descend on you like a ton of bricks,' " he said.

The Federal Deposit Insurance Corp. is due to unveil the proposal formally on Tuesday with votes by the Securities and Exchange Commission, the Federal Reserve and other regulators to follow. The draft asks for comments to be filed within 60 days, a period that could be extended.

Some details have been known for several weeks, but the American Banker on Oct. 5 posted a complete draft of the rule on its Web site.

Abernathy suggested that the proposal shows some of the same problems that were evident when former Fed Chairman Paul Volcker (pictured) first proposed the proprietary trading ban -- exactly what is banned isn't easy to define. Volcker, when asked to explain what would be blocked, said, "Bankers know what proprietary trading is and is not."

Abernathy said much of what is legal and what isn't is contextual and the lack of specifically banned activities could lead to confused banks shying from legal activities and investors shying away from banks. He said the rule would also force banks to take thousands of employees from normal work and turn them into "busybodies" whose only job is double-checking that banks aren't moving into proprietary trading areas.

Marcus Stanley, policy director of Americans for Financial Reform, a coalition of consumer and labor groups, said his group, too, is concerned about the lack of specifics about what's being banned. "We are both looking at the same core problem. There are very few bright lines." Stanley said his group is concerned that broad exemptions in the proposal for banks engaged in "liquidity management" and "securitization" and the lack of specifics could let banks engage in some of the same problematic practices that led to the Dodd-Frank law in the first place.

The proposal "is too weighted for preserving bank freedom, rather than creating the kinds of changes that are contemplated by the statute," he said. Stanley suggested the proposal in requiring a lot of documentation by banks without restraining banks' activities could be putting "form above substance," and he questioned whether it would have done much to prevent recent problems at UBS with a rogue trader.

The proposal, besides dealing directly with what banks can do, also imposes new limits on banks tying employee compensation to investment performance.