The middleman companies that manage drug benefits for millions of American workers are under growing pressure from government officials, big employers and some drug makers to end their practice of cutting secret deals with drug companies, deals that often favor sales of expensive drugs.

Already, some of the companies, known as pharmacy benefit managers, have made formal promises to inform their customers fully about any rebates or other deals they make with manufacturers.

More such moves could not only upend the industry's business model but result in substantially lower drug costs for employers and workers, according to industry executives and analysts. Because the companies are expected to manage the new Medicare drug benefit, the savings could extend to the elderly, as well.

The pressure on the benefit managers is taking several forms. Federal prosecutors who have been investigating the industry are offering briefings to employers on ways to demand more transparency in their drug plans. Big employers, including the Ford Motor Company and Verizon Communications, have been pressing in negotiations for the benefit managers to be more open or to eliminate their deals with manufacturers altogether.

Some drug manufacturers, meanwhile, are saying they have no objection to letting employers see their contracts with the pharmacy benefit managers, contradicting assertions by those companies that it is the manufacturers who have insisted on secrecy.