The largest adult foster care facility in the District of Columbia will go out of business by the end of the year because it cannot afford to take care of about 145 indegent people with a history of mental illness who reside in it on the payments it receives from the city.

For several years now, Earl F. Lovell, owner and operator of Fendall House, has joined other foster care sponsors in warning the city that they could not continue to provide services to indigents on the $180-per-person allotment they get to feed, clothe, house and supervise the mentally ill.

Lovell recently told the city he must close his two-building red-brick facility in Anacostia because he has lost $120,000 over the past three years.

Lovell's announcement came several days after a General Accounting Office report criticized St. Elizabeth's Hospital for not referring more than one-third of its mentally ill patients to non medical facilities like Fendall House that could care for them more cheaply than the hospital.

City officials said that the loss of Fendall House would worsen an already serious problem of too few homes to care for the mentally ill.

"The majority of residents in the District's adult foster care facilities are referrals from St. Elizabeth's or the Department of Human Resources," said Albert P. Russo, director of DHR.

"The loss of Fendall House - the largest - will create an extremely serious problem, and I am distressed that this is about to happen," Russo said.

While the city has increased its payments from $150 per patient - the rate offered these facilities since 1972 - to a new rate of $180 last year, Lovell said the increase is too little, too late.

"I have been to the City Council to the Congress, to the Department of Human Resources - anyone who will listen - to plead with them to please raise the rates to a reasonable level," said Lovell. "The city has demonstrated its complacency, and has not done anything for years in helping us help these people."

Russo said DHR and the City Council are working together to increase payments to adult foster care facilities, but for years, the city has lacked funds to increase the support payments.

A recent staff report by one of the City Council's committees recomended that payments to adult foster care facilities be increased by at least $70 per person each month. Lovell said the facilities need at least $450 to operate at a profit.

Of the $180 given to these facilities, $177,80 comes from the the federal government through supplemental security income payments. Russo said DHR provides and additional $2.20 to adult foster care homes and also gives the residents $30 a month for their personal needs.

In the District of Columbia, there are about 1360 adult foster home residents who receive benefits through the combined federal and District supplements.

It would cost St. Elizabeth's Hospital about $94 a day or nearly $3,000 a month per resident, to provide the same minimal level of supervision that adult foster homes offer for $180 a month, a hospital spokesman said.

A few law signed by Mayor Walter E. Washington that sets licensing standards that must be met by Oct. 1 by the city's approximately 500 adult foster-care facilities, homes for the elderly and half-way houses will create new hardships for these facilities, owners say.

While they agree that standards are endeed, owners have said that the standards in many cases, will require them to hire additional medical and dietary personnel, will require extensive record-keeping procedures on all residents, and will require expensive renovations that they can not afford on the amount of money they get from the city.

Lovell said that because of the size of his facility the new law would have required him to hire a full-time social worker, activities director, dietician consultant and an-call resident physician.

"The additional staff would have cost us about $80,000 a year," Lovell said. "We would also have to buy smoke detectors to met the law, and that would have cost about $4,000. I just can't afford it," he said.

Lovell, a retired Marine Lieutenant colonel who saw action in Korea and South Vietnam, said he is attempting to find homes for the middle-aged and elderly residents of Fendall House.