Two private firms that keep track of the District's 125,000 Medicaid recipients have assigned thousands of them to the wrong doctors and health plans in recent weeks, a series of foul-ups that disrupted some residents' medical care, city officials said yesterday.

The mistakes by computer operators invalidated health plan cards that people use to obtain medication or medical treatment and deprived the city's seven Medicaid health maintenance organizations of hundreds of thousands of dollars in revenue, officials said.

The mistakes could cost taxpayers as well. About 1,000 recipients were transferred out of the managed-care plans entirely and shifted into traditional fee-for-service coverage, which is potentially more costly than HMO care.

D.C. Public Health Director Ivan C.A. Walks said yesterday that the disruptions began in November and were not related to year 2000 changeover.

"Whether the problem is a patient not knowing where to go to get care or an HMO not being assigned patients and paid appropriately, we can't tolerate it," Walks said.

If the situation cannot be resolved quickly, he said, the city will replace one or both of the private firms.

One of the firms involved in the problems is the city's Medicaid enrollment broker, Benova, a national firm that has a city contract to track patient assignments and send them to "default" health plans when they don't choose a plan on their own.

The second firm is another national company, First Health, which as fiscal agent determines how much to pay health plans each month based on enrollment figures. Each Medicaid enrollee generates HMO fees of about $125 a month.

While no one was accidentally booted out of the Medicaid program entirely, the unexpected reassignments created confusion and frustration, several officials said.

They said a patient who suddenly encounters resistance from health providers is prone to avoid hassles by seeking care at a free clinic, where no one is turned away. That increases financial stress on those organizations, which are struggling to care for many of the District's 81,000 residents who have no health insurance.

"Patients think they don't have Medicaid, but they do," said Gloria WilderBraithwaite, a pediatrician who treats indigents at a mobile van in Southeast Washington. "It's causing the HMOs to make people think they are disenrolled when they aren't. . . . The HMOs don't try hard to help them understand what is happening."

HMO executives say they have seen dips in Medicaid payments to them; one health plan said it would receive about $100,000 less this month, and its staff is spending substantial time fielding telephone calls and sorting out mistaken assignments.

WilderBraithwaite said the resulting skittishness caused one HMO to defer a Medicaid patient's surgery, planned for late November, until enrollment computers confirmed that he was still enrolled in the health plan for December.

The problems began a few weeks after Herbert H. Weldon Jr. took over the D.C. Medicaid program in early November. That came after a number of high-level D.C. Medicaid officials departed and Benova was hired temporarily as an enrollment broker.

"The staff is working full speed on this to find out what the problem is," Weldon said yesterday. "We hope to have it corrected pretty soon. We've made an effort to talk to the HMOs and keep them informed, and reach out to the recipients to make sure they understood what is going on."

In one case, 1,551 D.C. residents were randomly assigned to one of the HMOs before the time had elapsed to choose one on their own. An additional 1,000 residents who returned to Medicaid coverage after leaving the program for a time were assigned to different doctors and health plans than they had before, improperly interrupting the continuity of their care, Walks said.

Finally, about 1,000 more patients were discharged from HMOs and put in the fee-for-service system, said Dawn Bartram, a Medicaid program analyst.

"We have stepped up aggressive outreach efforts" to alert recipients, she said. "But I have not heard of any clinical care compromises. We always make accommodations to get people to treatment."

It wasn't clear yesterday exactly why the mistakes were made, but they were human errors, not technological ones, Bartram said.

Benova and First Health are vying to win a contract from D.C. government as enrollment broker for a longer term beginning in April.

Officials at neither firm responded to calls for comment yesterday.