The U.S. Postal Service is growing more and more expensive and deaf to the general public as it reduces services under pressure from major business clients, a study sponsored by consumer advocate Ralph Nader charged yesterday.

The 515-page report, "The Postal Precipice," written by Kathleen Conkey of Nader's Center for Responsive Law, called the 11-year-old agency "a unique experiment, that of a monopoly without accountability which was supposed to achieve a pay-as-you-go self-sustaining status." Because of the drive toward this status, the study said, "the experiment has not worked well."

This view contrasts sharply with that of postal administrators, who proudly reported their second budgetary surplus last month and insist they are delivering more mail faster and more efficiently than ever before.

The study argued that financial independence is an unreasonable goal. "As labor, energy and other costs go up, management chooses to reduce service rather than press for even a modest public service subsidy," it said.

"Quantitatively, the postal subsidy is minuscule compared with the special interest subsidies to industry and commerce in this country. But philosophically it is taboo."

Business does not want to pay for services it does not need, the study said. But public outcry over occasional efforts to limit six-day delivery, to-the-door service, rural post offices and free home delivery have proved that "Americans want these services and are willing to shoulder a 'postal deficit' to have them," it said.

"When the users of the Postal Service are its only financial supporters, the largest and most powerful of those users will soon clamor to be its only decision-makers," it warned.