D.C. government health officials who failed to collect nearly $2.5 million in bills for medical services over the past three years are undertaking a belated attempt to get the money.

Beginning this week, letters asking for payment are to be sent to about 30,000 persons who accumulated 90,000 unpaid bills at neighborhood clinics, mental health clinics and D.C. Village, the city's home for the indegent elderly. A letter accompanying the bills says that failure to pay "may result" in referral of the accounts to a collection agency.

In announcing the campaign, James Buford, director of the Department of Human Services, said "it is essential that we make this collection effort to help the department meet its continuing service delivery responsibilities." But while the department, which overspent its budget by at least $18 million in the fiscal year that just ended, could certainly use the money, the collection of cash is a secondary purpose of the collection effort, according to officials involved in it.

The overriding purpose is to clear the city's books of unpaid bills so that private auditors hired by Congress can deliver a legally required audit by Feb. 1. That means the bills must either be collected or written off, and before they can be written off the city must demonstrate that it made a "good faith" effort to collect them.

Most of the bills were incurred by clients whose family incomes made them ineligible for Medicaid. Many of the clients, according to clinic workers, were pergnant teen-agers seeking prenatal care or elderly persons who may have since died or moved out of the city. "Sure there are some bad addresses," said Grady Williams, chief of DHS's bureau of payments and collections. "But many of these people have files with us for food stamps or welfare and we can cross-check them."

The direct-mail effort to collect the bills is part of an overall revision of DHS billing and accounting procedures developed by the accounting firm of Price, Waterhouse & Co. under a contract with the Temporary Commission on Financial Oversight, which was created to clean up the city's chaotic financial records. Medical care is among the most expensive services provided by the city to its residents and the facilities that provide it -- including the area clinics and D.C. General Hospital -- have a reputation for laxness in collecting their fees.

Services at municipal health facilities are not free, Williams said. Each patient is supposed to be informed at registration of what the costs will be, and rate schedules are supposed to be posted, he said.