The report commissioned by Wall Street's largest lobby group, the Securities Industry and Financial Markets Association (SIFMA), said banks play a small but vital role in the natural resources supply chain. Their ability to trade in the underlying commodities - not just financial derivatives - helped markets function.

"Banks play an essential role in assuring the smooth functioning of the commodity markets which underpin the $16.6 trillion U.S. economy, and on which consumers ultimately rely," said the report by IHS (>> IHS Inc.), a major global research, analysis and specialist information group that in recent years has bought some of the world's foremost energy consultancies.

The report comes weeks before the U.S. Senate Banking Committee is expected to hold its second hearing on the issue of Wall Street's deepened involvement in physical markets, which has come under intense public scrutiny over allegations that bank-owned metal warehouses have inflated prices.

Regulators and politicians are also questioning whether Wall Street's involvement in risky commercial activities could pose a threat to their financial soundness.

The Electric Power Supply Association (EPSA) also wrote an open letter to the Federal Reserve on Wednesday, asking the Fed to consider Wall Street's usefulness in electricity markets, in the first public sign that the banks' clients are concerned about losing access to the banks' services.

Electricity hedging and trading, "is best carried out in robust commodity markets that allow for and promote access to a variety of credit-worthy counterparties, including banks," the letter said.

EPSA's members include energy majors like BP Plc and Shell's North American arm, as well public power providers like New Jersey's PSE&G.

Federal Reserve officials go before lawmakers next month to explain why banks have been allowed to operate oil tankers, power plants and metal warehouses, the Fed is expected to make public key decisions about whether banks will be able to carry on trading as many have for a decade or more.

The IHS report warned that without the ability to trade in the real raw materials themselves, banks would likely either stop providing financial services to certain areas or industries, or be forced to raise fees.

"Physical commodity trade ? being able to (take) or make delivery of the underlying commodity ? is often required to provide these services. The consequences of impairing this role could be far-reaching and negative," it said.

WIDER BENEFITS

The IHS report was produced by eight senior IHS Global analysts and overseen by Daniel Yergin, who won a Pulitzer Prize in 1992 for his seminal history of the oil industry, "The Prize."

It uses five anonymous case studies to demonstrate how banks' involvement in physical commodity trading has benefited the wider economy, including jet fuel supply deals it says helped lower costs for a bankrupt airline, and trading and financing for struggling East Coast oil refineries.

"Capital intensive commodities industries require significant levels of investment in production, transport, processing and marketing facilities to bring energy and products to the American consumer," the report said. "Financial institutions are at the center of this activity."

IHS said that it believed the benefit of allowing banks to trade in physical markets was "significant," but did not attempt to estimate the overall economic or consumer impact.

In a report last year, IHS estimated that curbs on Wall Street's activities in physical markets created by the so-called Volcker Rule - designed to curb banks' trading with their own capital - could increase average gasoline prices on the East Coast by 4 cents a gallon.

Electric power costs in the United States could also increase by $5.3 billion a year, the 2012 report said.

The Federal Reserve has two critical decisions to make.

First it must decide whether former investment banks Goldman Sachs (>> Goldman Sachs Group Inc) and Morgan Stanley (>> Morgan Stanley) will be allowed to continue owning and operating physical assets like oil pipelines and metal warehouses, an activity explicitly prohibited for other banks. A five-year grace period following their conversion to bank holding companies expires this weekend.

The Fed is also expected soon to make clear the result of an unexpected "review" of its 2003 decision to allow commercial banks to trade in physical commodity markets.

JPMorgan Chase (>> JPMorgan Chase & Co) has already announced it plans to sell its physical commodity business in the face of mounting regulatory scrutiny, as Chief Executive Jamie Dimon attempts to pull the bank back from riskier, non-core businesses in the face of criticism it is still "too big to fail." But Goldman Sachs has remained resolute that its storied J Aron commodity arm is a "core" part of the bank.

(Reporting by David Sheppard; Editing by Jim Marshall, Nick Zieminski and Tim Dobbyn)

By David Sheppard