Consumer advocate Ralph Nader yesterday called for federal "Truth in Billing" legislation to rectify unfair and unethical billing practices and mistakes that he said cost consumers billions of dollars annually.

At an afternoon news conference in the District, Nader released the results of a five-month study that detailed billing practices such as fees for hospital tests that weren't performed and charges for unidentified services.

"The amount in question is sometimes just a few dimes, sometimes much more than a few dollars, but overall, consumers are being nickeled and dimed out of billions," Nader said.

The study, conducted under the auspices of Nader's Center for Study of Responsive Law, was based on examinations of 1,000 bills collected from consumers and small businesses across the country.

The study outlines six categories of routine billing procedures that Nader called part of a "massive, widespread fleecing" of consumers. They are unitemized and indecipherable bills, overcharges and phony charges, charges for processing, and the practice of charging customers interest on bills already identified as mistakes.

He cited processing charges -- what a customer pays for the cost of billing -- as "the latest wrinkle of computerized billing" and said the technology itself has helped open the way for billing errors and fraud.

"The computer almost mesmerizes people with its aura of officialdom," Nader said, calling "computer error" the most frequently used excuse for billing problems.

Nader said he wants Congress to enact legislation to standardize language used in bills, require itemization and mandate fines and civil damages against companies that refuse to correct their mistakes.

Currently, Nader said, the Fair Credit Reporting Act, which governs credit card billing practices, is the only law that addresses billing problems.