District residents who have joined Medicaid health maintenance organizations are spending half as much time in hospitals as they did when individual doctors were paid directly to arrange their care, city officials said yesterday.

That finding was part of the first public evaluation of the service offered by the seven HMOs that now provide health care to 72,600 of the District's 125,000 Medicaid recipients.

Since April 1998, hospital use by Medicaid HMO members has fallen to 334 days a year per 1,000 members, less than half the 670 hospital days per 1,000 spent by Medicaid recipients in 1996, when they could not join HMOs.

The comparison did not include disabled people and others whose hospital needs and medical costs are much higher.

The report by the Medicaid program illustrates how HMO cost-cutting policies avoid unnecessary care and help control spending but also how those policies contribute to the keen financial pressures threatening the District's 11 acute-care hospitals.

Partly because of those pressures, Mayor Anthony A. Williams (D) and other top city officials are trying to reform the city's health care system, which has too many empty hospital beds and not enough basic medical services for the uninsured.

D.C. Hospital Association officials questioned Medicaid's statistics, saying the drop-off in hospital use appears sharper than the association's information shows. They suggested more analysis.

While acknowledging that HMOs help with prevention, particularly for patients who don't have a regular doctor, the hospital association noted that "there have been enrollment difficulties," said Joan Lewis, the group's senior vice president. "People haven't been able to get to the plan they think they've enrolled in, and sometimes there are problems with reimbursement and payment."

The report said that Capital Community Health Plan had the highest member retention rate, 91 percent, followed by Chartered Health Plan, at 90 percent. Advantage Health Plan, with the lowest retention rate, lost more than half its members in a year.

George Washington University Health Plan had by far the worst telephone service, according to the report, with 27 percent of callers hanging up after being left on hold. The GWU plan said yesterday that member services have been revamped and callers now receive help on average in less than 20 seconds.

D.C. Medicaid Director Paul Offner said the report was not comprehensive but a first step toward assuring critics on the D.C. Council who say that Medicaid is not carefully managed.

"They have this notion that the HMO program in the District has continued to exist without any monitoring or performance oversight, and it's just not true," he said. "We've been doing this kind of stuff for a year and a half, but this is the first time we published anything."